Q1 general biology 2 mr. pabores

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Title Page
General Biology 2
Alvin A. Pabores, LPT
LAGUNA UNIVERSITY

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Table of Contents
Module 1: Genetics
Introduction
Lesson 1: Mendelian Genetics 4
Lesson 2. Patterns of Inheritance 11
Lesson 3. Gene Interactions 21
Lesson 4. Application of Recombinant DNA 34
Assessment Task 41
Summary 52
References 55
Module 2: Evolution and Origin of Biodiversity
Introduction
Learning Outcomes
Lesson 1. History of Life on Earth 59
Lesson 2. Mechanisms that Produce Change in
Populations 66
Lesson 3. Development of Evolutionary Thought 71
Lesson 4. Patterns of Descent with Modification 80
Lesson 5. Evidences of Evolution 87
Assessment Task 98
Summary 110
References 115
Y
Module 3: Systematics Based on Evolutionary Relationships
Introduction
Learning Outcomes
Lesson 1. 3-Domain Scheme and 5-Kingdom Scheme 118
Lesson 2. Based on Evolutionary Relationships:
Taxonomy 125
Lesson 3. Phylogenetic tree and Cladogram 132
Assessment Task 135
Summary 140
References 144

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ubject Code: GB2
Subject Code: Gen Bio 2
Course Description: This subject is designed to enhance the
understanding of the principles and concepts in the study of biology,
particularly heredity and variation, and the diversity of living organisms,
their structure, function, and evolution..
Content Standards:
The learners demonstrate an understanding of:
1. recombinant DNA;
2. relevance, mechanisms, evidence/bases, and theories of evolution;
3. basic taxonomic concepts and principles, description, nomenclature,
identification, and classification;
4. plant and animal organ systems and their functions; and
5. feedback mechanisms.
Performance Standards:
The learners shall be able to:
1. make a research paper/case study/poster on genetic diseases;
2. make a diagram (e.g., pictogram, poster) showing the evolution of a
domesticated crop;
3. differentiate the 3-domain scheme from the 5-kingdom scheme of
classification of living things; and
4. develop a presentation (e.g. role-playing, dramatizationand other forms
of multimedia) to show how an organism maintains homeostasis
through the interaction of the various organ systems in the body.
Subject Requirements:
 Assessment Tasks
 Written Works -25%
 Performance Tasks (Activity) -45%
 Quarterly Exam -30%
Quarterly Grade 100%
Final Grade = (First Quarter Grade + Second Quarter Grade)/2

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MODULE 1
GENETICS
Introduction
Notice that a mango tree can only produce mango fruits, a dog can only produce
puppies, and human beings can only produce infants. The offsprings always have likeness
to the parents in certain major respects and variation from the parents in many minor
respects. The traits are transmitted from parents to offsprings by means of the information
stored in molecules called DNA. The passing of traits from parents to offspring is called
heredity.
The information stored in the DNA is essential for life. If a cell dies the body must
replace that cell. The only way to replace the cells is to first copy the information that the cell
contained. There is a complex system of proteins and enzymes that unravel the DNA double
helix so that the DNA can be copied. If a single cell dies it can be replaced through mitosis.
The two daughter cells are identical to the original cell whose DNA was copied. This system
works well with single cell and simple organisms. More complex organisms use meiosis to
produce gametes (egg or sperm cells) for sexual reproduction. Meiosis also begins with
DNA replication. Each gamete has half the amount of DNA as the parent cell. When a
sperm fertilizes the egg, a new cell containing a complete copy of DNA forms for that
species forms, called a zygote.
DNA replication is the process by which DNA makes a copy of itself during cell
division.
1. The first step in DNA replication is to ‘unzip’ the double helix structure of the
DNA molecule.
2. This is carried out by an enzyme called helicase which breaks the hydrogen
bonds holding the complementary bases of DNA together (A with T, C with G).
3. The separation of the two single strands of DNA creates a ‘Y’ shape called a
replication ‘fork’. The two separated strands will act as templates for making
the new strands of DNA.
4. One of the strands is oriented in the 3’ to 5’ direction (towards the replication
fork), this is the leading strand. The other strand is oriented in the 5’ to 3’
direction (away from the replication fork), this is the lagging strand. As a result of
their different orientations, the two strands are replicated differently:

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Figure 1. Replication of the Leading and Lagging Strands of DNA
8. Once all of the bases are matched up (A with T, C with G), an enzyme called
exonuclease strips away the primer(s). The gaps where the primer(s) were are
then filled by yet more complementary nucleotides.
9. The new strand is proofread to make sure there are no mistakes in the new DNA
sequence.
10. Finally, an enzyme called DNA ligase? seals up the sequence of DNA into two
continuous double strands.
11. The result of DNA replication is two DNA molecules consisting of one new and
one old chain of nucleotides. This is why DNA replication is described as semi-
conservative, half of the chain is part of the original DNA molecule, half is brand
new.
12. Following replication the new DNA automatically winds up into a double helix.
The result of DNA replication is two DNA molecules consisting of one new and one
old chain of nucleotides. This is why DNA replication is described as semi-conservative, half
of the chain is part of the original DNA molecule, half is brand new.
Learning Outcomes
At the end of this module, learners should be able to:
1. outline the processes involved in genetic engineering. (STEM_BIO11/12-IIIa-b-6);
2. discuss the applications of recombinant DNA, (STEM_BIO11/12-IIIa-b-7); and
3. predict genotypes and phenotypes of parents and offspring using the laws of inheritance.
(STEM_BIO11/12-IIIa-b-1)
Leading Strand:
5. A short piece of RNA called a primer
(produced by an enzyme called primase)
comes along and binds to the end of the
leading strand. The primer acts as the
starting point for DNA synthesis.
6. DNA polymerase binds to the leading
strand and then ‘walks’ along it,
adding new complementary nucleotide
bases (A, C, G and T) to the strand of
DNA in the 5’ to 3’ direction.
7. This sort of replication is called
continuous.
Lagging strand:
5. Numerous RNA primers are made by
the primase enzyme and bind at
various points along the lagging strand.
6. Chunks of DNA, called Okazaki
fragments, are then added to the
lagging strand also in the 5’ to 3’
direction.
7. This type of replication is called
discontinuous as the Okazaki
fragments will need to be joined up
later.
Source: https://www.yourgenome.org/facts/what-is-dna-replication

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4. Differentiates the types of allelic and non-allelic gene interactions.
5. Perform a calculations about the Mendelian and Gene Interactions.
Lesson 1: Mendelian Genetics
Gregor Mendel was an Austrian monk who discovered the basic principles of
heredity through experiments in his garden. Mendel's observations became the foundation
of modern genetics and the study of heredity, and he is widely considered a pioneer in the
field of genetics. He is known as the "father of modern genetics," was born in Austria in
1822. A monk, Mendel discovered the basic principles of heredity through experiments in his
monastery's garden. His experiments showed that the inheritance of certain traits in pea
plants follows particular patterns, subsequently becoming the foundation of modern genetics
and leading to the study of heredity.
Source: https://www.biography.com/scientist/gregor-mendel
Figure 2: Gregor Mendel
Around 1857, Mendel began breeding garden peas (Pisum sativum) in the abbey
garden to study inheritance. Mendel probably chose to work with peas is that there are
many varieties. A heritable feature that varies among individuals, such as flower color, is
called a character. Each variant for a character, such as purple or white color for flowers, is
called a trait. The following are characters of garden pea and the dual nature of its traits.
 Flower color (white or purple)
 Pea shape (round or wrinkled)
 Flower position (axial or terminal)
 Plant height (short or tall)
 Seed (wrinkle or smooth)
 Pod shape (inflated or constricted)
 Pod color (yellow or green)

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Source: https://tinyurl.com/yyfamqrb
Figure 3. List of Contrasting Characters of Garden Pea
The following are essential terminologies in understanding the key principles of
Mendelian inheritance
Alleles. The alleles for a trait occupy the same locus or position on homologous
chromosomes and thus govern the same trait. However, because they are different, their
action may result in different expressions of that trait.
Carrier. An individual who is heterozygous for a trait that only shows up in the
phenotype of those who are homozygous recessive. Carriers often do not show any signs
of the trait but can pass it on to their offspring.
Cross-pollination. The mating of two genetically different plants of the same species.
Usually, the term is used in reference to the crossing of two pure breeding (homozygous)
plants.
Dominant allele. An allele that masks the presence of a recessive allele in the
phenotype. Dominant alleles for a trait are usually expressed if an individual is
homozygous dominant or heterozygous.
F1 generation. The first offspring (or filial) generation. The next and subsequent
generations are referred to as F2, F3, etc.
Genes. Units of inheritance usually occurring at specific locations, or loci, on a
chromosome. Physically, a gene is a sequence of DNA bases that specify the order of
amino acids in an entire protein or, in some cases, a portion of a protein. A gene may be
made up of hundreds of thousands of DNA bases. Genes are responsible for the hereditary
traits in plants and animals.
Genotype. Genetic makeup of an individual. Genotype can refer to an organism's
entire genetic makeup or the alleles at a particular locus. (T, t)
Heterozygous. Consisting of two different alleles of a gene for a particular trait (Tt).
Individuals who are heterozygous for a trait are referred to as heterozygotes.
Homozygous. Having the same allele at the same locus on both members of a pair
of homologous chromosomes. Homozygous also refers to a genotype consisting of two
identical alleles of a gene for a particular trait. An individual may be homozygous dominant

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(TT) or homozygous recessive (tt). Individuals who are homozygous for a trait are referred
to as homozygotes. See heterozygous.
Hybrids. Offspring that are the result of mating between two genetically different
kinds of parents--the opposite of purebred.
Phenotype. The observable or detectable characteristics of an individual organism--
the detectable expression of a genotype. T is the genotype and tall is the phenotype while t
is the genotype and short is the phenotype.
Purebred. Offspring that are the result of mating between genetically similar kinds of
parents--the opposite of hybrid. Purebred is the same as true breeding.
Mendel’s Experimental, Quantitative Approach
Mendel could strictly control mating between plants. Each pea flower has both
pollen-producing organs (stamens) and an egg-bearing organ (carpel). In nature, pea plants
usually self-fertilize: Pollen grains from the stamens land on the carpel of the same flower,
and sperm released from the pollen grains fertilize eggs present in the carpel. To achieve
cross-pollination of two plants, Mendel removed the immature stamens of a plant before
they produced pollen and then dusted pollen from another plant onto the altered flowers.
Each resulting zygote then developed into a plant embryo encased in a seed (pea). His
method allowed Mendel to always be sure of the parentage of new seeds.
Source: Campbell Biology, Eleventh Edition
Figure 4. When F1 hybrid pea plants cross-pollinate, Traits appear
in
the F2 generation
Mendel conducted two main experiments to determine the laws of inheritance. These
experiments were: monohybrid cross experiment and dihybrid cross experiment
Mendel experimented on a pea plant and considered 7 main contrasting traits in the
plants. Then, he conducted both the experiments to determine the aforementioned
inheritance laws. A brief explanation of the two experiments is given below.
The two experiments lead to the formulation of Mendel’s laws known as laws of
inheritance which are:

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Law of Dominance. This is also called as Mendel’s first law of inheritance. According
to the law of dominance, hybrid offsprings will only inherit the dominant trait in the
phenotype. The alleles that are suppressed are called as the recessive traits while the
alleles that determine the trait are known as the dominant traits.
Figure. 5. Example of Law of Dominance
Law of Segregation. The law of segregation states that during the production of
gametes, two copies of each hereditary factor segregate so that offspring acquire one factor
from each parent. In other words, allele (alternative form of the gene) pairs segregate during
the formation of gamete and re-unite randomly during fertilization. This is also known as
Mendel’s third law of inheritance.
Figure 6. Example of Law of Segregation
Law of Independent Assortment. Also known as Mendel’s second law of inheritance,
the law of independent assortment states that a pair of trait segregates independently from
another pair during gamete formation. As the individual heredity factors assort
independently, different traits get equal opportunity to occur together.

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Figure 7. Example of Law of Independent Assortment
The Testcross
The test cross is an experiment first employed by Gregor Mendel, in his studies of
the genetics of traits in pea plants. Mendel’s theory, which holds true today, was that each
organism carried two copies of each trait. One was dominant trait, while one could be
considered recessive. The dominant trait, if present, would determine the outward
appearance of the organism, or the phenotype. Thus, Mendel became interested in the
question of determining which organisms with the dominant phenotype had two dominant
alleles, and which have one dominant allele and one recessive allele. His answer came in
the form of the test cross.
Monohybrid Cross
The typical example of the test cross is the origin experiment Mendel conducted
himself, to determine the genotype of a yellow pea. As seen in the image below, the alleles
Y and y are used for the yellow and green versions of the allele, respectively. The yellow
allele, Y, is dominant over the y allele. Therefore, in an organism with the genotype Yy, only
the yellow allele is seen in the phenotype. Mendel had a yellow pea, and he wanted to know
whether it was YY or Yy.
Source: https://biologydictionary.net/test-cross/
Figure 8. Mendel bred the unknown yellow pea (Y?) with a
green
pea, being homozygous recessive (yy).
Dihybrid Test Cross
This simple model works well for a single trait, but it can easily be expanded to
encompass more traits. The dihybrid cross is a cross which looks at the cross of two
separate traits with different alleles. Sticking with the pea color example, we will add a trait
to the cross, let’s say shape. Peas can either be round and plump, or wrinkly. Round peas
are dominant, created by the (R) allele. Wrinkled peas are only found in homozygous
recessive individuals (rr). The following chart shows how to calculate the results of test
cross. (Note that wrinkled seeds should have the r allele).

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Source: https://biologydictionary.net/test-cross/
Figure 9. Dihybrid cross of RRYY x rryy
Lesson 2. Patterns of Inheritance
It is important to understand the basic laws of inheritance to appreciate how
conditions are passed on in a family. An accurate family health history is a valuable tool to
illustrate how conditions are passed down through generations. The inheritance patterns of
single gene diseases are often referred to as Mendelian since Gregor Mendel first observed
the different patterns of gene segregation for selected traits in garden peas and was able to
determine probabilities of recurrence of a trait for subsequent generations. If a family is
affected by a disease, an accurate family history will be important to establish a pattern of
transmission. In addition, a family history can even help to exclude genetic diseases,
particularly for common diseases where behavior and environment play strong roles.
The expression of the mutated allele with respect to the normal allele can be
characterized as dominant, co-dominant, or recessive. There are five basic modes of
inheritance for single-gene diseases: X-linked dominant, X-linked recessive, Y-linked traits,
(collectively known as Sex-Linked Traits) autosomal dominant, autosomal recessive,and
mitochondrial.
Sex-Linked Traits
Sex-linked traits are genetic characteristics determined by genes located on sex
chromosomes. Sex chromosomes are found within our reproductive cells and determine the
sex of an individual. Traits are passed on from one generation to the next by our genes.
Genes are segments of DNA found on chromosomes that carry information for protein
production and that are responsible for the inheritance of specific traits. Genes exist in
alternative forms called alleles. One allele for a trait is inherited from each parent. Like traits
that originate from genes on autosomes (non-sex chromosomes), sex-linked traits are
passed from parents to offspring through sexual reproduction.
Sex Cells
Organisms that reproduce sexually do so via the production of sex cells, also called
gametes. In humans, male gametes are spermatozoa (sperm cells) and female gametes are
ova or eggs. Male sperm cells may carry one of two types of sex chromosomes. They either
carry an X chromosome or a Y chromosome. However, a female egg cell may carry only an
X sex chromosome. When sex cells fuse in a process called fertilization, the resulting cell

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(zygote) receives one sex chromosome from each parent cell. The sperm cell determines
the sex of an individual. If a sperm cell containing an X chromosome fertilizes an egg, the
resulting zygote will be (XX) or female. If the sperm cell contains a Y chromosome, then the
resulting zygote will be (XY) or male.
Source: https://tinyurl.com/y3zuh3ds
Figure 10. Male sperm cells fertilizing a female egg
Sex-linked Genes
Genes that are found on sex chromosomes are called sex-linked genes. These
genes can be on either the X chromosome or the Y chromosome.
 If a gene is located on the Y chromosome, it is a Y-linked gene. These genes
are only inherited by males because, in most instances, males have a
genotype of (XY). Females do not have the Y sex chromosome.
 Genes that are found on the X chromosome are called X-linked genes, its
either X-linked dominant traits or X-linked recessive traits. These genes can
be inherited by both males and females.
X-linked recessive traits
An example of X-linked recessive traits can be seen in hemophilia. Hemophilia is a
blood disorder in which certain blood clotting factors are not produced. This results in
excessive bleeding that can damage organs and tissues. Hemophilia is an X-linked
recessive trait caused by a gene mutation. It is more often seen in men than women.
Source: https://ghr.nlm.nih.gov/condition/hemophilia
Figure 11. Impaired blood clotting in hemophilia

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The inheritance pattern for the hemophilia trait differs depending on whether or not
the mother is a carrier for the trait and if the father does or does not have the trait. If the
mother carries the trait and the father does not have hemophilia, the sons have a 50/50
chance of inheriting the disorder and the daughters have a 50/50 chance of being carriers
for the trait. If a son inherits an X chromosome with the hemophilia gene from the mother,
the trait will be expressed and he will have the disorder. If a daughter inherits the mutated X
chromosome, her normal X chromosome will compensate for the abnormal chromosome
and the disease will not be expressed. Although she will not have the disorder, she will be a
carrier for the trait.
Source: //istudy.pk/x-linked%E2%80%82recessive%E2%80%82disorders/hemophilia/
Figure 12. X-linked recessive inheritance scenarios for either the mother
being a
carrier or the father being affected
If the father has hemophilia and the mother does not have the trait, none of the sons
will have hemophilia because they inherit a normal X chromosome from the mother, who
does not carry the trait. However, all of the daughters will carry the trait as they inherit an X
chromosome from the father with the hemophilia gene.
X-linked dominant traits
In X-linked dominant traits, the phenotype is expressed in both males and females
who have an X chromosome that contains the abnormal gene. If the mother has one
mutated X gene (she has the disease) and the father does not, the sons and daughters
have a 50/50 chance of inheriting the disease. If the father has the disease and the mother
does not, all of the daughters will inherit the disease and none of the sons will inherit the
disease.

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Source: https://ghr.nlm.nih.gov/primer/inheritance/inheritancepatterns
Figure 13. X-linked dominant inheritance scenarios
Fragile X syndrome is a genetic condition that causes a range of developmental
problems including learning disabilities and cognitive impairment. Usually, males are more
severely affected by this disorder than females. Fragile X syndrome is inherited in an X-
linked dominant pattern. A condition is considered X-linked if the mutated gene that causes
the disorder is located on the X chromosome, one of the two sex chromosomes. (The Y
chromosome is the other sex chromosome.) The inheritance is dominant if one copy of the
altered gene in each cell is sufficient to cause the condition. X-linked dominant means that
in females (who have two X chromosomes), a mutation in one of the two copies of a gene in
each cell is sufficient to cause the disorder. In males (who have only one X chromosome), a
mutation in the only copy of a gene in each cell causes the disorder. In most cases, males
experience more severe symptoms of the disorder than females.
Source: https://w iki.ubc.ca/Course:MEDG550/Student_Activities/Fragile-X_Syndrome
Figure 14. Symptoms of Fragile X
Y-linked traits
Y-linked traits never occur in females, and occur in all male descendants of an
affected male. The concepts of dominant and recessive do not apply to Y-linked traits, as
only one allele (on the Y) is ever present in any one (male) individual. Males with a single Y-
or X-linked allele are described as hemizygotes, because only one allele is present.
A condition is considered Y-linked if the mutated gene that causes the disorder is
located on the Y chromosome, one of the two sex chromosomes in each of a male's cells.
Because only males have a Y chromosome, in Y-linked inheritance, a mutation can only be
passed from father to son.
Hypertrichosis is an excessive growth of hair on a particular area of the body which
is abnormal for the age, sex or race of an individual. The presence of the excessive coarse
black hair on the auricle of the human ear is referred to as hypertrichosis pinnae auris or
hairy ears. The condition is primarily restricted to older men and occasionally observed in
females. According to the available literature, hypertrichosis pinnae auris is a Y-linked
character.

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Source: Source: https://ghr.nlm.nih.gov/primer/inheritance/inheritancepatterns
Figure 15. Y-linked traits scenarios
Source: https://tinyurl.com/y5hxcthw
Figure 16. Hypertrichosis Pinnae Auris
Other Patterns of Inheritance
Autosomal dominant
One mutated copy of the gene in each cell is sufficient for a person to be affected by
an autosomal dominant disorder. In some cases, an affected person inherits the condition
from an affected parent. In others, the condition may result from a new mutation in the gene
and occur in people with no history of the disorder in their family.
Huntington disease is a progressive brain disorder that causes uncontrolled
movements, emotional problems, and loss of thinking ability (cognition). This condition is
inherited in an autosomal dominant pattern, which means one copy of the altered gene in
each cell is sufficient to cause the disorder. An affected person usually inherits the altered
gene from one affected parent. In rare cases, an individual with Huntington disease does not
have a parent with the disorder.
Source: https://www.mayoclinic.org/autosomal-dominant-inheritance pattern/img-20006210
Figure 17. Autosomal dominant inheritance pattern

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Source: https://tinyurl.com/y4ogx2fj
Figure 18. Effect of Huntington’s Disease
Autosomal recessive
In autosomal recessive inheritance, both copies of the gene in each cell have
mutations. The parents of an individual with an autosomal recessive condition each carry
one copy of the mutated gene, but they typically do not show signs and symptoms of the
condition. Autosomal recessive disorders are typically not seen in every generation of an
affected family.
Sickle cell disease is a group of disorders that affects hemoglobin, the molecule in
red blood cells that delivers oxygen to cells throughout the body. People with this disorder
have atypical hemoglobin molecules called hemoglobin S, which can distort red blood cells
into a sickle, or crescent, shape. Signs and symptoms of sickle cell disease usually begin in
early childhood. Characteristic features of this disorder include a low number of red blood
cells (anemia), repeated infections, and periodic episodes of pain. This condition is inherited
in an autosomal recessive pattern, which means both copies of the gene in each cell have
mutations. The parents of an individual with an autosomal recessive condition each carry
one copy of the mutated gene, but they typically do not show signs and symptoms of the
condition.
Source: https://tinyurl.com/yxqgu8u2
Figure 19. Autosomal recessive inheritance pattern

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Source: https://utsw med.org/medblog/how -does-sickle-cell-anemia-affect-pregnancy/
Figure 20. Comparison of Normal RBC and Sickle Cell
Mitochondrial inheritance
Also known as maternal inheritance, applies to genes in mitochondrial DNA.
Mitochondria, which are structures in each cell that convert molecules into energy, each
contain a small amount of DNA. Because only egg cells contribute mitochondria to the
developing embryo, only females can pass on mitochondrial mutations to their children.
Conditions resulting from mutations in mitochondrial DNA can appear in every generation of
a family and can affect both males and females, but fathers do not pass these disorders to
their daughters or sons.
Source: https://en.w ikipedia.org/w iki/Human_mitochondrial_genetics
Figure 21. Mitochondrial inheritance patterns
Lesson 3. Gene Interactions
Mendelian genetics does not explain all kinds of inheritance for which the phenotypic
ratios in some cases are different from Mendelian ratios (3:1 for monohybrid, 9:3:3:1 for di-
hybrid in F2). This is because sometimes a particular allele may be partially or equally
dominant to the other or due to existence of more than two alleles or due to lethal alleles.
These kinds of genetic interactions between the alleles of a single gene are referred to as
allelic or intra- allelic interactions. Non-allelic or inter-allelic interactions also occur where the
development of single character is due to two or more genes affecting the expression of
each other in various ways.

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Thus, the expression of gene is not independent of each other and dependent on the
presence or absence of other gene or genes; These kinds of deviations from Mendelian one
gene-one trait concept is known as Factor Hypothesis or Interaction of Genes
Allelic Gene Interactions
Incomplete Dominance or Blending Inheritance (1:2:1)
A dominant allele may not completely suppress other allele, hence a heterozygote is
phenotypically distinguishable (intermediate phenotype) from either homozygotes. In
snapdragon and Mirabilis jalapa, the cross between pure bred red-flowered and white-
flowered plants yields pink-flowered F1 hybrid plants (deviation from parental phenotypes),
i.e., intermediate of the two parents. When F1 plants are self-fertilized, the F2 progeny
shows three classes of plants in the ratio 1 red: 2 pink: 1 white instead of 3:1.
Source: https://w w w .slideshare.net/BobbyPabores1/genetics-stem12
Figure 22. Inheritance of flower color in snapdragon
Therefore, a F1 di-hybrid showing incomplete dominance for both the characters will
segregate in F2 into (1 :2 : 1) X (1 :2 : 1 ) = 1 :2 : 1 : 2 : 4 : 2:1 : 2 : 1. And a F1 di-hybrid
showing complete dominance for one trait and incomplete dominance of another trait will
segregate in F2 into (3:1) x (1 :2:1) = 3:6:3:1:2:1.
Co-dominance
Here both the alleles of a gene express themselves in the heterozygotes.
Phenotypes of both the parents appear in F1 hybrid rather than the intermediate phenotype.
In human, MN blood group is controlled by a single gene.
Only two alleles exist, M and N. Father with N blood group (genotype NN) and
mother with M blood group (genotype MM) will have children with MN blood group
(genotype MN). Both phenotypes are identifiable in the hybrid. F2 segregates in the ratio 1M
blood group: 2 MN blood group : 1 N blood group.

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Lethal Factor (2:1)
The genes which cause the death of the individual carrying it, is called lethal factor.
Recessive lethals are expressed only when they are in homozygous state and the
heterozygotes remain unaffected. There are genes that have a dominant phenotypic effect
but are recessive lethal, e.g., gene for yellow coat colour in mice.
But many genes are recessive both in their phenotypic as well as lethal effects, e.g.,
gene producing albino seedlings in barley.
Figure 23. Inheritance of lethal gene in mice and barley
Two Main Types of Lethal Factor
1. Dominant lethal alleles. Mutation of wild type allele; removed from population in
same generation.
Source. https://w w w .slideshare.net/BobbyPabores1/genetics-stem12
Figure 24. Dominant lethal allele in Huntington’s disease
2. Recessive lethal alleles. No obvious phenotypic affect in heterozygotes; unique
phenotype in heterozygotes.
Figure 25. Recessive lethal allele in Agouti coat coloration
Multiple Allele
A gene for particular character may have more than two allelomorphs or alleles
occupying same locus of the chromosome (only two of them present in a diploid organism).

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These allelomorphs make a series of multiple alleles. Human ABO blood group system
furnishes best example. The gene for antigen may occur in three possible allelic forms – lA,
IB, i. The allele for the A antigen is co-dominant with the allele I8 for the B antigen. Both are
completely dominant to the allele i which fails to specify any detectable antigenic structure.
Therefore, the possible genotypes of the four blood groups are shown in Fig. 26.
Figure 26. ABO blood groups and their genotypes in
human
Non Allelic Gene Interactions
Simple Interaction (9:3:3:1)
In this case, two non-alleiic gene pairs affect the same character. The dominant
allele of each of the two factors produces separate phenotypes when they are alone. When
both the dominant alleles are present together, they produce a distinct new phenotype. The
absence of both the dominant alleles gives rise to yet another phenotype.
The inheritance of comb types in fowls is the best example where R gene gives rise
to rose comb and P gene gives rise to pea comb; both are dominant over single comb; the
presence of both the dominant genes results in walnut comb. Similar pattern of inheritance
is found in Streptocarpus flower color (Fig. 27).
Figure 27. Inheritance of comb types in fowl

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Source: https://tinyurl.com/yxgkqhq7
Figure 28. Four comb phenotypes in chickens explained by
segregation at the Rose-comb and Pea-comb loci and their
interaction. (A) Single-combed, (B) Rose-combed, (C) Pea-
combed male, and (D) walnut-combed male.
Figure 29. Inheritance of flower color in Streptocarpus
Complementary Factor (9:7)
Certain characters are produced by the inter-action between two or more genes
occupying different loci inherited from different parents. These genes are complementary to
one another, i.e., if present alone they remain unexpressed, only when they are brought
together through suitable crossing will express.
In sweet pea (Lathyrus odoratus), both the genes C and P are required to synthesize
anthocyanin pigment causing purple colour. But absence of any one cannot produce
anthocyanin causing white flower. So C and P are complementary to each other for
anthocyanin formation (Fig.30).

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Figure 30. Inheritance of flower color in Lathyrus odoratus
Epistasis
When a gene or gene pair masks or prevents the expression of other non-allelic
gene, called epistasis. The gene which produces the effect called epistatic gene and the
gene whose expression is suppressed called hypostatic gene.
Recessive Epistasis or Supplementary Factor (9:3:4). In this case, homozygous
recessive condition of a gene determines the phenotype irrespective of the alleles of other
gene pairs, i.e., recessive allele hides the effect of the other gene. The coat colour of mice is
controlled by two pairs of genes. E.g. Dominant gene C produces black colour, absence of
it causes albino. Gene A produces agouti colour in presence of C, but cannot express in
absence of it (with cc) resulting in albino. Thus recessive allele c (cc) is epistatic to dominant
allele A (Fig. 31).
Source: Source. https://w w w .slideshare.net/BobbyPabores1/genetics-stem12
Figure 31. Inheritance of coat in mice
The grain colour in maize is governed by two genes — R (red) and Pr (purple). The
reces-sive allele rr is epistatic to gene Pr (Fig. 29).

20
Figure 32. Inheritance of grain color in maize
Dominant Epistasis (12:3:1). Sometimes a dominant gene does not allow the
expression of other non-allelic gene called dominant epistasis. In summer squash, the fruit
colour is governed by two genes. The dominant gene W for white colour, suppresses the
expres-sion of the gene Y which controls yellow colour. So yellow colour appears only in
absence of W. Thus W is epistatic to Y. In absence of both W and Y, green colour develops.
Figure 33. Inheritance of fruit color in summer squash
Inhibitory Factor
Inhibitory factor is such a gene which itself has no phenotypic effect but inhibits the
expres-sion of another non-allelic gene; in rice, purple leaf colour is due to gene P, and p
causing green colour. Another non-allelic dominant gene I inhibits the expression of P but is
ineffective in recessive form (ii). Thus the factor I has no visible effect of its own but inhibits
the colour expression of P (Fig. 34).
Figure 34. Inheritance of leaf color in rice
Inhibitory Factor with Partial Dominance (7:6:3)
Sometimes an inhibitory gene shows incomplete dominance thus allowing the
expression of other gene partially. In guinea pig, hair direction is controlled by two genes.
Rough (R) hair is dominant over smooth (r) hair, other gene I is inhibitory to R at
homozygous state (II) but in heterozygous state (II) causes partially rough (Fig. 35).

21
Figure 35. Inheritance of hair in guinea pig
Polymorphic Gene (9:6:1)
Here two non-allelilc genes controlling a character produce identical phenotype when
they are alone, but when both the genes are present together their phenotypes effect is
enhanced due to cumulative effect. In barley, two genes A and B affect the length of awns.
Gene A or B alone gives rise to awns of medium length (the effect of A is same as B); but
when both present, long awn is produced; absence of both results awnless (Fig. 7.13).
Figure 36. Inheritance of coat color in mice
Duplicate Gene (15:1)
Sometimes a character is controlled by two non-allelic genes whose dominant alleles
produce the same phenotype whether they are alone or together. In Shepherd’s purse
(Capsella bursa-pastoris), the presence of either gene A or gene B or both results in
triangular capsules; when both these genes are in reces-sive forms, the oval capsules
produced (Fig. 34).

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Figure 37. Inheritance of capsule shape in Shepherd’s purse
Duplicate Gene with Dominance Modification (11:5)
A character controlled by two gene pairs showing dominance only if two dominant
alleles are present. Dominant phenotype will thus be produced only when two non-allelic
dominant alleles or two allelic dominant alleles are present. Such a case is found in pigment
glands of cotton (Fig. 35).
Figure 38. Inheritance of pigment glands in cotton
Other Kinds of Gene Interactions
Modifiers. Genes which modify the phenotypic effect of a major gene called
modifying gene. They reduce or enhance the effect of other gene in quantitative manner,
e.g., genes responsible for dilution of body colour.
Suppressors. Genes which will not allow mutant allele of another gene to express
resulting in wild phenotype called suppressor gene, e.g., Su-s in Drosophila suppresses the
expression of dominant mutant gene star eye(s).
Pleiotropy. Gene having more than one effect (multiple effects) are called pleiotropic
genes. They have a major effect in addition to secondary effect. In Drosophila, the genes for
bristle, eye and wing significantly influence the number of facets in bar-eyed individuals.
Atavism. The appearance of offspring’s which resemble their remote ancestors
called atavism.

23
Penetrance. The ability of a gene to be expressed phenotypically to any degree is
called penetrance. Penetrance may be complete, e.g., in pea, expression of R allele for red
flower in homozygous and heterozygous conditions. It may be incomplete, e.g., dominant
gene P for Polydactyly in human, sometimes does not show polydactylous condition in
heterozygous state.
Lesson 4. Application of Recombinant DNA
Genetic engineering refers to the direct manipulation of DNA to alter an organism’s
characteristics (phenotype) in a particular way.
 Genetic engineering, sometimes called genetic modification, is the process of
altering the DNA in an organism’s genome.
 This may mean changing one base pair (A-T or C-G), deleting a whole region
of DNA, or introducing an additional copy of a gene.
 It may also mean extracting DNA from another organism’s genome and
combining it with the DNA of that individual.
 Genetic engineering is used by scientists to enhance or modify the
characteristics of an individual organism.
 Genetic engineering can be applied to any organism, from a virus to a sheep.
 For example, genetic engineering can be used to produce plants that have a
higher nutritional value or can tolerate exposure to herbicides.
To help explain the process of genetic engineering we have taken the example of
insulin, a protein that helps regulate the sugar levels in our blood.
 Normally insulin is produced in the pancreas, but in people with type 1
diabetes there is a problem with insulin production.
 People with diabetes therefore have to inject insulin to control their blood
sugar levels.
 Genetic engineering has been used to produce a type of insulin, very similar
to our own, from yeast and bacteria like E. coli.
 This genetically modified insulin, ‘Humulin’ was licensed for human use in
1982.
The Genetic Engineering Process
1. A small piece of circular DNA called a plasmid (a small, circular, double-stranded
DNA molecule that is distinct from a cell's chromosomal DNA) is extracted from
the bacteria or yeast cell.
2. A small section is then cut out of the circular plasmid by restriction enzymes,
‘molecular scissors’.
3. The gene for human insulin is inserted into the gap in the plasmid. This plasmid
is now genetically modified.
4. The genetically modified plasmid is introduced into a new bacteria or yeast cell.

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5. This cell then divides rapidly and starts making insulin.
6. To create large amounts of the cells, the genetically modified bacteria or yeast
are grown in large fermentation vessels that contain all the nutrients they need.
The more the cells divide, the more insulin is produced.
7. When fermentation is complete, the mixture is filtered to release the insulin. The
insulin is then purified and packaged into bottles and insulin pens for distribution
to patients with diabetes.
Source: https://w w w .yourgenome.org/facts/w hat-is-dna-replication
Figure 39. Genetic Engineering Process
Genetically Modified Organisms (GMOs)
GMOs are organisms that have had their characteristics changed through the
modification of their DNA. With the ability to insert gene sequences, comes the possibility of
providing new traits for these target organisms. This has allowed the development of GMOs.
Some of these genetic modifications promise higher product yield for their targets. These
include the Flavr-Savr Tomato and Bt-Corn.
The Flavr-Savr (“Flavor Savor”) tomato was the first genetically modified organism
that was licensed for human consumption. The trait modified in this tomato is its ripening
process. A gene for an enzyme that causes the degradation of pectin in the cell walls (i.e.
polygalacturonase) normally softens the fruit as it ripens. In Flavr Savr tomatoes, an inhibitor
(i.e. antisense RNA) disrupts the expression of this gene, thereby delaying the softening of
the fruit and extending the time it may be kept in storage and transported to markets.

25
Source: https://flavrsavrtomato.w eebly.com/pros-cons-and-my-view s.html
Figure 40. Flavr-Savr Tomato
Bt-Corn was developed to incorporate the production of a toxin (i.e. Bt-endotoxin)
from Bacillus thuringensis in corn plants. This toxin results in the death of pests that feed on
these plants like the corn borer larvae. The toxin has been shown to be selective for
Lepidoptera larvae and is non-toxic to humans, mammals, fish and birds. The selective
toxicity of the toxin allows its use in food crops. The introduction of the toxin is believed to
increase crop production due to decreased losses from pest infestation. The same
technology has been applied in the Philippines for the development of Bt-Eggplant.
Source: https://medium.com/@arringtoncea/gmo-corn-savior-or-destroyer-1f2990316902
Figure 41. Bt-Corn comparison to native corn
Featherless chickens could be the future of mass poultry farming in warmer
countries, says an Israeli geneticist who has created a bare-skinned “prototype”. The new
chicken would be lower in calories, faster-growing, environmentally friendly, and more likely
to survive in warmer conditions, claims Avigdor Cahaner of the Hebrew University of
Jerusalem. He created his red-skinned chicken by selectively crossing a breed with a
naturally bare neck with a regular broiler chicken. But critics say past experience with
feather-free chickens resulting from random genetic mutation shows they suffer more than
normal birds. Males have been unable to mate, because they cannot flap their wings, and
“naked” chickens of both sexes are more susceptible to parasites, mosquito attacks and
sunburn.
Source: https://nextnature.net/2006/10/featherless-chicken
Figure 42. Featherless chickens
Pig-primate chimeras have been born live for the first time but died within a week.
The two piglets, created by a team in China, looked normal although a small proportion of
their cells were derived from cynomolgus monkeys. The ultimate aim of the work is to grow
human organs in animals for transplantation. But the results show there is still a long way to
go to achieve this, the team says. According to Dr. Tang Hai at the State Key Laboratory of
Stem Cell and Reproductive Biology in Beijing that this is the first report of full-term pig-

26
monkey chimeras. Hai and his colleagues genetically modified cynomolgus monkey cells
growing in culture so they produced a fluorescent protein called GFP. This enabled the
researchers to track the cells and their descendents. They then derived embryonic stem
cells from the modified cells and injected them into pig embryos five days after fertilization.
Golden Rice, which was developed in the hopes of combatting that problem by a
team of European scientists in the late '90s, was genetically modified to provide an essential
nutrient that white rice lacks: beta-carotene, which is converted into vitamin A in the body.
But the golden rice was banned particularly in the Philippines. A quick evidence check is
sufficient to reveal the simple reason why golden rice is not for farmer’s fields: it is still not
ready because it is not performing agronomically. Furthermore, it is far from being medically
documented to relieve symptoms of Vitamin A deficiency.
Source: http://tiny.cc/wz4ksz
Figure 43. Anti-GMO network protests Golden Rice
commercialization in Philippines
DNA recombination
DNA recombination is a process in which specialized proteins interact with DNA to
create molecules with altered base sequence content. Depending on the details of the
reaction, the outcomes are deletions, duplications or simply a new order of allelic variation.
The most common classification of DNA recombination is general or homologous
recombination occurs between DNA molecules of very similar sequence, such as
homologous chromosomes in diploid organisms. General recombination can occur
throughout the genome of diploid organisms, using one or a small number of common
enzymatic pathways.
Site-specific recombination occurs at a specific DNA sequence. The first example
was found in the integration between λ DNA and E. coli DNA. Both of them contain a
sequence, 5'-TTTATAC-3', called the attachment site, which allows the two DNA molecules
to attach together by base pairing. Once attached, the enzyme integrase catalyzes two
single strand breaks as in the Holliday model. After a short branch migration, the integrase
exerts a second strand cuts on two other strands. Resolution of two Holliday junctions
completes the integration process.

27
Source: https://www.web-books.com/MoBio/Free/Ch8D2.htm
Figure 44. Site-specific recombination between λ DNAand
E. coli DNA
The widely accepted model for DNA cross-over was first proposed by Robin Holliday
in 1964. It involves several steps as illustrated in the figure. Two homologous DNA
molecules line up (e.g., two nonsister chromatids line up during meiosis).
1. Cuts in one strand of both DNAs.
2. The cut strands cross and join homologous strands, forming the Holliday
structure (or Holliday junction).
3. Heteroduplex region is formed by branch migration.
4. Resolution of the Holliday structure. Figure. e is a different view of the Holliday
junction than Figure d. DNA strands may be cut along either the vertical line or
horizontal line.
5. The vertical cut will result in crossover between f-f' and F-F' regions. The
heteroduplex region will eventually be corrected by mismatch repair.
6. The horizontal cut does not lead to crossover after mismatch repair. However, it
could cause gene conversion.

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Source: https://www.web-books.com/MoBio/Free/Ch8D2.htm
Figure 45. The Holliday model of DNA crossover showing the homologous
recombination
Precise genome editing has been a long standing goal in the field of biology which
has been achieved with the help of engineered nucleases like CRISPR and TALENs. With
recent improvements in gene therapy, the reality of creating designer babies is closer than
ever, with procedures like CRISPR or TALENs. On one hand, this will help prevent babies
from being born with genetic diseases. But how many traits should parents be allowed to
pick and choose? The ethics of this genetic engineering procedure has been the topic of
much debate and has created a dilemma for some. With the ability to pick and choose which
traits they like, parents could alter the intelligence, health, size, gender and many other
characteristics of their child. Could designer babies change society forever? What do you
think? Open the link below: "Designer Babies: The Science and Ethics of Genetic
Engineering ". Retrieved on June 23, 2020 from
https://www.youtube.com/watch?v=k1a2larfMIA
Table 1. Advantages and Disadvantages of Genetic Engineering
Genetic Engineering
Advantages Disadvantages
Task 1
Genetic Engineering: Pros & Cons
Through genetic engineering, scientists are able to move desirable genes from
one plant or animal to another or from a plant to an animal or vice versa. By desirable, it
means it can produce an outcome that is regarded as generally “beneficial” or
“useful”. Not every scientific discovery has a happy ending. There are always
unintended consequences for this discovery.
List three advantages and disadvantages of using genetic engineering.
AssessmentTask

29
Written Works 1
Mendelian and Non-Mendelian Genetics
For each problem, fill in all the requested information. Support your work
by illustrating the crosses using Punnett squares.
1. In dogs, wire hair (H) is dominant to smooth (s). In a cross of a homozygous
wire-haired dog with a smooth-haired dog what would be
Genotype of offspring:
Phenotype of offspring:
Punnet square:
2. Carnegiea gigantea or commonly known as Saguaro cacti are tall dessert
plants that usually have two L-shaped arms. Suppose you visit Sonoran
Dessert where the Saguaro cactus is common and you take a picture of the
tallest Saguaro cactus. Your Saguaro has two arms but one is longer than
the other. Now, assume that arm length in these cacti are controlled by a
single gene with arms of the same length (A) being dominant to arms of
different lengths (a).
What is the genotype of the tallest cactus that you have taken a picture?
If the tallest cactus pollinate a cactus that is heterozygous for arms of the
same length what would be…
Genotype of offspring:

30
Phenotype of offspring:
Punnet square:
3. In humans freckles (F) are dominant to no freckles (f). Also, hairy toes (T)
are dominant to non-hairy toes (t). Cross a homozygous freckled,
heterozygous hairy toed male with a non-freckled and homozygous hairy
toed female.
a. What percent of the offspring will have the genotype FFTt?
b. What percent of the offspring will be heterozygous for both traits?
c. What percent of the offspring will be non-freckled with hairy toes?
Punnet square:
4. In sheep wool color is controlled by one gene and only two alleles. There
are three genotypes (BB, Bb, and bb) and three phenotypes (black, grey and
white) for wool color. The female sheep with color grey wool mate with male
sheep with homozygous recessive color of wool.
a. What is the specific type of gene interaction shown in item no. 3?
b. What is the genotype of offspring?
c. What is the phenotype of offspring?
Punnet square:
5. In cats, there is a gene which produces ticked fur (bands of different colors
on each hair) called agouti (H). The recessive allele (h) for this gene
produces hair which is a solid color brown from end to end. In addition, there
is a coat color gene which has a recessive albino allele (a) which, in the
homozygote, prevents the production of any coat color pigment, resulting in
a white cat with pink eyes, the traditional albino. Note that this problem has
described two completely different genes. These genes are unlinked. An

31
albino female cat is mated to a solid brown male cat. All of their offspring are
Agouti. The males and females among these offspring are allowed to freely
intermate, producing a flock of F2 kittens.
a. What is the specific type of gene interaction shown in item no. 5?
b. How many solid brown fur cat(s) produce in mating?
c. What is/are the genotype(s) to express the agouti color of cat?
d. Predict the phenotypic ratio for fur color among these many
grandkittens.
Punnet square:
Written Works 2
Direction: Read each item carefully and encircle the correct answer.
1. What is the reason of the scientist in developing the Flavr-Savr tomato?
A. to retain its natural color and flavour
B. to identify the possible effect of tomato
C. to transport the tomato in market easily
D. to reproduce enough tomato for human consumption
2. Below is a piece of the gene sequence that encodes for the insulin protein.
5`-CAG-CCG-CAG-CCT-TTG-TGA-ACC-AAC-ACC-TGT-GCG-GCT-CAC
-ACC-TGG-TGG-3`
The piece of gene sequence for the insulin change to...
5`-CAG-CCG-CAG-CCT-TTG-TGA-ACC-AAC-ACC-TGT-GCG-GCT-
CAC-ACC-CAG-TGG-TGG-3`
Can we considered the additional triple codon as beneficial for the insulin
protein?
A. No, because the triple codon may alters the insulin protein.
B. No, because the insulin protein makes its own triple codon.
C. Yes, because the additional triple codon can make additional
characteristics.
D. Yes, because the insulin protein needs a lot of triple codon.

32
3. What is the first step in exchanging of DNA molecules occur in
homologous recombination?
A. heteroduplex migration exchange the DNA molecules
B. joining the homologous strand
C. DNA molecules line up
D. vertical and horizontal cut of heteroduplex region
4. In order to perform the site-specific recombination, what should be the
similarity of λ DNA and the host organism?
A. presence of integrase
B. able to undergo holliday junctions
C. similar sequence of codons
D. able to replicate via DNA recombination
5. The following are some of genetically mutations of featherless chickens
EXCEPT
A. prone from different parasites
B. unable to reproduce
C. vulnerable to radiation
D. can’t survive in warn condition
6. According to Mendel’s law of segregation…
A. there is a 50% probability that a gamete will get a dominant allele
B. gene pairs segregate independently of other genes in gamete formation.
C. allele pairs separate in gamete formation.
D. there is a 3:1 ration in the F2 generation.
7. What is the inheritance pattern when both alleles are expressed equally in
the phenotype of a heterozygote?
A. multiple alleles C. incomplete dominance
B. codominance D. lethal factors
8. Looking at your dog will give information concerning…
A. the dog’s genotype C. the dog’s phenotype
B. the dog’s recessive alleles D. the dog’s heterozygous alleles
9. What percentage of the possible offspring will be hybrids?
A. 25% C. 50%
B. 75% D. 100%
10. In the ABO blood group system in humans, if a person of type-B blood
has children with a person of type-AB blood, what blood types could their
children have?
A. Type-AB, type-A, and type-B
B. Type-B and type-AB
C. Type-AB, type-A, type-B, and type-O
D. Type-A and type-B

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11. In a cross of AaBb x AaBb, what fraction of the offspring can be
expected to express one of the two heterozygous dominant alleles?
A. 9/16 C. 1/2
B. 3/8- D. 3/16
12. The X-linked recessive trait of color-blindness is present in 5% of males.
If a mother who is a carrier and father who is unaffected plan to have one
children, what is the probability the children will both be color-blind?
A. 50% C. <1%
B. 25% D. 12.5%
13. In a cross involving two heterozygous parents, which is the chance of the
offspring having the dominant phenotype?
A. 25% C. 50%
B. 75% D. 100%
14. Which of the following is part of the law of segregation?
I. there are two factors controlling a given traits
II. one factor is dominant over the other factor
III. the two factors separate into different gametes.
A. 1 and 2 C. 1 and 3
B. 2 and 3 D. 1, 2, and 3
15. Assume tall (T) is completely dominant to dwarf (t) in a certain species of
plant. If a homozygous dominant individual is crossed with a homozygous
dwarf, the offspring will …
A. be one-half tall and one-half dwarf
B. all be short
C. be three-quarters tall and one-quarter dwarf
D. all be tall
16. Pea plants are tall if they have the genotype TT or Tt, and they are short
if they have genotype tt. A tall plant is mated with a short plant. Which
outcome below would indicate that the tall parent plant was heterozygous?
A. The ratio of tall offspring to short offspring is 3:1.
B. The ratio of tall offspring to short offspring is 50%-50%. -
C. All of the offspring are short.
D. All of the offspring are tall.
17. If each parent can produce 100 genetically distinct gametes, how many
genetically distinct offspring can two parents produce?
A. 100 C. 200
B. 1,000- D. 10,000
18. If a heterozygous plant is allowed to self-pollinate, what proportion of
theoffspring will also be heterozygous?
A. 1/4 C. 1/3
B. 1/2 D. all of the plant

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19. A red chestnut coat horse is crossed with a white horse and all of the
offspring are roan, an intermediate color that is caused by the presence of
both red and white hairs. This is an example of genes that are …
A. polygenic C. completely dominant
B. epistatic D. codominant
20. A calico cat shows both the traits for orange fur and black fur. What kind
of allele expression is this?
A. incomplete dominance C. co-dominance
B. sex-linked inheritance D. gene inheritance
21. If there are 2 alleles for a trait, and one has the ability to totally "cover
up" the other, the one that can be "covered up" is called ...
A. dominant C. recessive
B. heterozygous D. homozygous
22. A boy from Africa is born with an extra finger on one hand known as
polydactly. Extra digits are common in members of the father's extended
family, but not the mother's. The boy's two older sisters have normal
fingers. What is the most likely explanation?
A. X-linked inheritance, since only males are affected
B. Y-linked inheritance: Males inherit from their fathers
C. The extra finger trait is autosomal dominant-
D. A spontaneous mutation occurred
23. A mother with type A blood and a father with type B blood have six
children with blood of type O and one blood type AB. Explain.
A. three different gene loci cause A, B, and O type
B. the parents are genotype AO and BO
C. O blood type shows partial penetrance
D. O blood type shows partial expressivity
24. If a gene is found only on the X chromosome and not the Y
chromosome, it is said to be what?
A. sex-linked trait C. gene inheritance
B. codominant trait D. incomplete dominance trait
25. In a dihybrid cross, the allele W and R are needed to produced red
flower and if one of the dominant allele is absent the flower turns to
orange. The homozygous recessive for both genotype (wwrr) represents
yellow color of the flower. What gene interaction express in this situation?
A. epistatsis C. codominance
B. polymorphic gene- D. inhibitory factor
26. Based on item no. 25, if the WWRR and the yellow color mate, How
many orange flower may produced in F2 generation?
A. 6 C. 1
B. 3 D. 12

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27. If the allele for tounge rolling is represented as "T" it would mean that...
A. T is a recessive trait
B. the gene for tounge rolling is carried on the maternal chromosome
C. the gene for tounge rolling is carried on the paternal chromosome
D. tounge rolling is a dominant trait
28. Which among the following is the best example of codominance?
A. blood types C. comb of the rooster
B. sickle cell anemia D. summer squash
29. Your brother has blue iris like his ancestors but your father, grandfather,
and great grandfather have dark iris. This is best example of…
A. atavism C. penetrance
B. pleiotropy D. expressivity
30. A Polish marries a Filipina and both do not show any apparent traits of
inherited disease. Six sons and three daughters are born, and four of their
sons suffer from a disease and fortunately none of the daughters is
affected. The following mode of inheritance for the disease is…
A. sex-linked recessive C. sex-linked dominant
B. autosomal dominant D. autosomal dominant
Summary
 Gregor Mendel, the Father of Genetics” was an Austrian monk who discovered
the basic principles of heredity through experiments in his garden
 Mendel began breeding garden peas (Pisum sativum), The characters of garden
pea are flower color, pea shape, flower position, plant height, seed, pod shape
and pod color.
 Mendel conducted two main experiments to determine the laws of inheritance.
These experiments were: monohybrid cross experiment and dihybrid cross
experiment
 According to the law of dominance, hybrid offsprings will only inherit the
dominant trait in the phenotype.
 Law of segregation states that during the production of gametes, two copies of
each hereditary factor segregate so that offspring acquire one factor from each
parent.
 Law of independent assortment states that a pair of trait segregates
independently from another pair during gamete formation. As the individual
heredity factors assort independently, different traits get equal opportunity to
occur together.
 A monohybrid cross involves a single parent, whereas a dihybrid cross involves
two parents and monohybrid cross produces a single offspring, whereas a
dihybrid cross produces two offspring.
 There are five basic modes of inheritance for single-gene diseases: X-linked
dominant, X-linked recessive, Y-linked traits, (collectively known as Sex-Linked
Traits) autosomal dominant, autosomal recessive,and mitochondrial.

36
 Sex-linked traits are genetic characteristics determined by genes located on sex
chromosomes.
 If a gene is located on the Y chromosome, it is a Y-linked gene. These genes are
only inherited by males because, in most instances, males have a genotype of
(XY). Females do not have the Y sex chromosome.
 Genes that are found on the X chromosome are called X-linked genes, its either
X-linked dominant traits or X-linked recessive traits. These genes can be
inherited by both males and females.
 Autosomal dominant and autosomal recessive affected the male and female.
 In autosomal dominant successive generations affected until no one inherits the
mutation while autosomal recessive can skip generation. ]
 Mitochondrial inheritance is the inheritance of a trait encoded in the mitochondrial
genome.
 Genetic engineering refers to the direct manipulation of DNA to alter an
organism’s characteristics (phenotype) in a particular way.
 A plasmid a small, circular, double-stranded DNA molecule that is distinct from a
cell's chromosomal DNA.
 GMOs are organisms that have had their characteristics changed through the
modification of their DNA.
 Bt-Corn was developed to incorporate the production of a toxin (i.e. Bt-endotoxin)
from Bacillus thuringensis in corn plants.
 The Flavr-Savr (“Flavor Savor”) tomato was the first genetically modified
organism that was licensed for human consumption.
 Featherless chickens is lower in calories, faster-growing, environmentally
friendly, and more likely to survive in warmer conditions but critics say past
experience with feather-free chickens resulting from random genetic mutation.
 Pig-primate chimeras aim to grow human organs in animals for transplantation
and have been born live for the first time but died within a week.
 Golden Rice, which was developed in the hopes of combating that problem by a
team of European scientists in the late '90s, was genetically modified to provide
an essential nutrient that white rice lacks: beta-carotene, which is converted into
vitamin A in the body.
 DNA recombination is a process in which specialized proteins interact with DNA
to create molecules with altered base sequence content.
 The most common classification of DNA recombination is general or homologous
recombination occurs between DNA molecules of very similar sequence, such as
homologous chromosomes in diploid organisms.
 Site-specific recombination occurs at a specific DNA sequence.
 Gene interactions occur when two or more allelic or non-allelic genes of same
genotype influence the outcome of particular phenotypic characters.
 Table 2. Different Types of Allelic and Non-Allelic Gene Interactions
Type Ratio Interaction Example
A. Allelic
Interactions
1. Incomplete
Dominance
a. Monohybrid
b. Dihybrid
1:2:1
1:2:1:2:4:2:1:2:1
Partial dominance
Partial dominance at
both the gene pairs.
Flower color in
snapdragon
Human blood group
(ABO)

37
2. Codominance
3. Lethal factor
4. Multiple alleles
3:6:3:1:2:1
1:2:1
2: 1/ 3:0
---
Complete dominance at
one gene pair and partial
dominance at the other.
Both the alleles of a
gene express
themselves in the
heterozygotes.
Homozygous condition
causes death.
Occurrence of more than
two alleles in a single
locus.
Cattle (horn and
hair color)
MN Blood Group
Yellow Coat color in
mice, albino
seedling in barley.
ABO blood group
system human, self
sterility in tobacco.
B. Non-allelic
Interactions
5. Simple
Interactions
6. Complementary
factor
7. Epsistasis
a. Recessive
b. Dominant
8. Inhibitory factor
9. Polymorphic
gene
10. Duplicate
gene
9:3:3:1
9:7
9:3:4
12:3:1
13:1
9:6:1
15:1
New phenotypes
resulting from interaction
between two dominants
and also between two
recessives.
Two dominant genes are
complementary to each
other in their effect.
A homozygous
recessive gene is
epistatic to other gene.
A dominant gene is
epistatic to other gene.
One dominant gene
inhibits the expression of
the other.
New phenotype from
interaction between two
dominant genes.
Dominant allele of either
gene pair, alone or
together,are similar in
phenotypic effect.
Comb types in fowl,
Streptocarpus flower
color.
Flower color in
sweet pea.
Coat color in mice,
grain color in maize.
Fruit color in
summer squash.
Leaf color in rice.
Awn length in
barley.
Capsule shape in
Shepherds purse.
References
 BiologyWise. “Three Domains of Life.” Biology Wise, 3 June 2011,
biologywise.com/three-domains-of-life. Accessed 25 July 2020.
 Bobby Pabores. “Genetics Stem-12.” SlideShare, 14 June 2019,
www.slideshare.net/BobbyPabores1/genetics-stem12. Accessed 25
July 2020.
 Buerstedde, Jean-Marie. “DNARecombination.” Encyclopedic Reference of
Genomics and Proteomics in Molecular Medicine, vol. 3, no. 1, 2020,

38
pp. 440–443, link.springer.com/referenceworkentry/10.1007%2F3-540
29623-9_2430, 10.1007/3-540-29623-9_2430. Accessed 22 July 2020.
 Genetics Home Reference. “What Are the Different Ways in Which a Genetic
Condition Can Be Inherited?” Genetics Home Reference, 2019,
ghr.nlm.nih.gov/primer/inheritance/inheritancepatterns. Accessed 24
July 2020.
 Page, Michael Le. “Exclusive: Two Pigs Engineered to Have Monkey Cells Born
in China.” New Scientist, 19 June 2019,www.newscientist.com/article
/2226490-exclusive-two-pigs-engineered-to-have-monkey-cells-born
in-china/. Accessed 19 June 2020.
 Reece, Jane B, et al. Campbell Biology. 11th ed., Don Mills, Ontario, Pearson
Canada Inc, 2015.
 Samanthi. “Difference Between Kingdom and Domain.” Compare the Difference
Between Similar Terms, 7 Nov. 2011, www.differencebetween.com/
difference-between-kingdom-and-vs-domain/. Accessed 26 July 2020.
 Siyavula. “Five Kingdom System | Biodiversity And Classification | Siyavula.”
Siyavula.Com, Siyavula, 2019, www.siyavula.com/read/science/grade-
10-lifesciences/biodiversity-and-classification/09-biodiversity-and-
classification-04. Accessed 26 July 2020.
 TeacherPH.com. “General Biology 2: Senior High School SHS Teaching Guide.
TeacherPH, 10 June 2017, www.teacherph.com/general-biology-2-
teaching-guide/. Accessed 22 July 2018.
 Your Genome. “What Is DNA Replication?” Your Genome, 25 Jan. 2016,
www.yourgenome.org/facts/what-is-dna-replication. Accessed 23 June
2020.
 Your Genome. What Is Genetic Engineering? 17 Feb. 2017,
www.yourgenome.org/facts/what-is-genetic-engineering. Accessed 24
June 2020.
 Web Books Publishing. “The Holliday Model of DNA Crossover.” Www.Web
Books.Com, 25 Feb. 2015, www.webbooks.com/MoBio/Free/Ch8D2
.htm. Accessed 23 June 2020.
 Wikipedia Contributors. “Phylogenetic Tree.” Wikipedia, Wikimedia
Foundation,
19 Sept. 2019, en.wikipedia.org/wiki/Phylogenetic_tree. Accessed 26 July
2020.

39
MODULE 2
EVOLUTION AND ORIGIN OF BIODIVERSITY
Introduction
Between 5 and 4.5 billion years ago, Earth formed when dust and rocks in the solar
system condensed. Earth's early atmosphere differed from today's in many ways, such as
the absence of both oxygen and a protective ozone layer. The seas that formed from
condensed water vapor contained dissolved minerals and gases. Most scientists agree that
the origin of Iife required the completion of four steps: simple organic molecules, polymers,
protocells and cells.
A fossil is a remnant, or the moulding, of an animal or a plant preserved in a
sedimentary rock. Fossils are very useful to the study of tectonic history. When a fossil of a
given species is found on several modern continents, it gives a strong indication that these
continents were previously unified. Fossils are also used to date sedimentary rocks. Some
species with a broad distribution on Earth and a short-term life (Ammonites for instance) are
great indicators to identify certain geological periods. Finally, fossils show us the long history
of life and the past and current evolution processes on Earth. The fossil records are like a
book unraveling the different shapes life forms took to adapt to Geologic Time Scale.
When we study the Earth’s age, we are also studying the fossil record and
ultimately, the theory of evolution. The Earth is approximately 4.6 billion years old – a very
big number ordinary humans can’t easily relate with, especially, the specific time frame
when we appeared.

40
With the aid of this module we will identify the genesis of life, genetic mechanisms
that cause change in populations, patterns of descent with modification and the scientists
and their respective contributions in the development of evolutionary thought.
Learning Outcomes
At the end of this module, learners should be able to:
1. describe general features of the history of life on Earth, including generally accepted
dates and sequence of the geologic time scale and characteristics of major groups of
organisms present during these time periods. (STEM_BIO11/12-IIIc-g-8);
2. explain the mechanisms that produce change in populations from generation to
generation (e.g., artificial selection, natural selection, genetic drift, mutation,
recombination). (STEM_BIO11/12-IIIc-g-9);
3. show patterns of descent with modification from common ancestors to produce the
organismal diversity observed today. (STEM_BIO11/12-IIIc-g-10);
4. trace the development of evolutionary thought. (STEM_BIO11/12-IIIc-g-11);
5. explain evidences of evolution (e.g., biogeography, fossil record, DNA/protein sequences,
homology, and embryology). (STEM_BIO11/12-IIIc-g-12); and
6. infer evolutionary relationships among organisms using the evidence of
evolution.(STEM_BIO11/12-IIIc-g-13)
Lesson 1.History of Life on Earth
Earth is estimated to be 4.54 billion years old, plus or minus about 50 million
years. Scientists have scoured the Earth searching for the oldest rocks to radiometrically
date. In northwestern Canada, they discovered rocks about 4.03 billion years old. Then, in
Australia, they discovered minerals about 4.3 billion years old. Researchers know that rocks
are continuously recycling, due to the rock cycle, so they continued to search for data
elsewhere. Since it is thought the bodies in the solar system may have formed at similar
times, scientists analyzed moon rocks collected during the moon landing and even
meteorites that have crash-landed on Earth. Both of these materials dated to between 4.4
and 4.5 billion years.
Geological Time Scale
The geologic time scale (GTS) is a system of chronological dating that relates
geological strata (stratigraphy) to time. It is used by geologists, paleontologists, and other
Earth scientists to describe the timing and relationships of events that once occurred, also
allowing them to accurately file the times when different creatures were fossilized, after
carbon dating.
The Geologic Time Scale is the history of the Earth broken down into four spans of
time marked by various events, such as the emergence of certain species, their evolution,
and their extinction, that help distinguish one era from another. Strictly speaking,
Precambrian Time is not an actual era due to the lack of diversity of life, however, it's still

41
considered significant because it predates the other three eras and may hold clues as to
how all life on Earth eventually came to be.
Precambrian Time: 4.6 billion to 542 Million Years Ago
Precambrian Time started at the beginning of the Earth 4.6 billion years ago. For
billions of years, there was no life on the planet. It wasn't until the end of Precambrian Time
that single-celled organisms came into existence. No one is certain how life on Earth began,
but theories include the Primordial Soup Theory, Hydrothermal Vent Theory, and
Panspermia Theory.
 The idea of the Primordial Soup Theory was originally proposed by Alexander
Oparin and John Haldane as a possible explanation for the creation of life on our
planet. The theory states that if energy is added to the gases that made up
Earth's early atmosphere, the building blocks of life would be created.
 The Deep Sea Vents or the Hydrothermal Vent Theory tells that the ocean are
quite fascinating because of how chemically diverse these vents are. The sea
vents are varying in pH, meaning there are a lot of electron transferring and
redox reactions. These acidic and basic environments allow for spontaneous
energy-producing reactions, which can lead to the possible formation of an
amino acid (which means proteins and then life). There have been a lot of
observation that organisms can evolve near or around these vents.
 Panspermia is a Greek word that translates literally as "seeds everywhere". The
panspermia theory states that the "seeds" of life exist all over the Universe and
can be propagated through space from one location to another. Some believe
that life on Earth may have originated through these "seeds". Mechanisms for
panspermia include the deflection of interstellar dust by solar radiation pressure
and extremophile microorganisms traveling through space within an asteroid,
meteorite or comet.
The end of this time span saw the rise of a few more complex animals in the oceans,
such as jellyfish. There was still no life on land, and the atmosphere was just beginning to
accumulate the oxygen required for higher-order animals to survive. Living organisms
wouldn't proliferate and diversify until the next era.
Paleozoic Era: 542 Million to 250 Million Years Ago
The Paleozoic Era began with the Cambrian Explosion, a relatively rapid period of
speciation that kicked off a long period of life flourishing on Earth. Vast amounts of life forms
from the oceans moved onto the land. Plants were the first to make the move, followed by
invertebrates. Not long afterward, vertebrates took to the land. Many new species appeared
and thrived. The end of the Paleozoic Era came with the largest mass extinction in the
history of life on Earth, wiping out 95% of marine life and nearly 70% of life on land. Climate
changes were most likely the cause of this phenomenon as the continents all drifted
together to form Pangaea. As devastating this mass extinction was, it paved the way for new
species to arise and a new era to begin.

42
Source: http://tiny.cc/m45ksz
Figure 46. Early Organism during the Paleozoic Era
Mesozoic Era: 250 Million to 65 Million Years Ago
After the Permian Extinction caused so many species to go extinct, a wide variety of
new species evolved and thrived during the Mesozoic Era, which is also known as the "age
of the dinosaurs" since dinosaurs were the dominant species of the age.
The climate during the Mesozoic Era was very humid and tropical, and many lush,
green plants sprouted all over the Earth. Dinosaurs started off small and grew larger as the
a. Cambrian
First Fishes: Early fish from the fossil record are
represented by a group of small, jawless,
armored fish known as ostracoderm.
First chordates.
b. Ordovician
Sudden diversion of Metazoan families
c. Silurian
First Vascular Land Plants: The earliest known
representatives of this group are placed in
genus Cooksonia
d. Devonian
First Amphibians: These ancient lobe-finned fish
had evolved multi-jointed leg-like fins with digits
that enabled them to crawl along the sea
bottom; Jawed fishes diversify
e. Carboniferous
Mississippian Scale Trees and seed ferns
Pennsylvanian--First reptile: the first reptiles
evolved from advaced reptiliomorpha
labyrinthodonts
d.Permian
Major extinctions: The occurred about 252 Ma,
forming the boundary between the Permian and
Triassic geologic periods, as well as the
Paleozoic and Mesozoic eras; Reptiles Diversify
Table 3. Periods under the Paleozoic era

43
Mesozoic Era went on. Herbivores thrived, small mammals came into existence, and birds
evolved from the dinosaurs.
Another mass extinction marked the end of the Mesozoic Era, whether triggered by a
giant meteor or comet impact, volcanic activity, more gradual climate change, or various
combinations of these factors. All the dinosaurs and many other animals, especially
herbivores, died off, leaving niches to be filled by new species in the coming era.
The climate during the Mesozoic Era was very humid and tropical, and many lush,
green plants sprouted all over the Earth. Dinosaurs started off small and grew larger as the
Mesozoic Era went on. Herbivores thrived, small mammals came into existence, and birds
evolved from the dinosaurs.
Another mass extinction marked the end of the Mesozoic Era, whether triggered by a
giant meteor or comet impact, volcanic activity, more gradual climate change, or various
combinations of these factors. All the dinosaurs and many other animals, especially
herbivores, died off, leaving niches to be filled by new species in the coming era.
Table 4. Periods under the Mesozoic era
a.Triassic
First Mammals: The first placental
mammals appeared at the beginning of
the Cretaceous period. The earliest
mammals were tiny, shrew-like
mammals.; First Dinosaurs; Eoraptor is
one of the earliest know dinosaurs.
b. Jurassic
First Birds: The earliest known is
Archaeopteryx lithographica, from late
Jurassic Period, though Archaeopteryx is
not commonly considered to have been
a true bird. Dinosaurs Diversify.
c. Cretaceous
Extinctions of Dinosaurs: It is thought
that a asteroid impact event may have
caused the extinction of the dinosaurs.;
First Primates; First Flowering Plants; A
plant that had no petals and lived
underwater more than 125 Ma could be
the oldest known 'flower', according to
scientists.
Cenozoic Era: 65 Million Years Ago to the Present

44
The final time period on the Geologic Time Scale is the Cenozoic Period. With large
dinosaurs now extinct, smaller mammals that had survived were able to grow and become
dominant. The climate changed drastically over a relatively short period of time, becoming
much cooler and drier than during the Mesozoic Era. An ice age covered most temperate
parts of the Earth with glaciers, causing life to adapt relatively rapidly and the rate of
evolution to increase. All species of life—including humans—evolved into their present-day
forms over the course of this era, which hasn't ended and most likely won't until another
mass extinction occurs.
Table 5. Periods under the Mesozoic era
a. Palegene and Neogene
Mammal Diversify: Mammals and
birds continued to evolve into
roughly modern forms, while other
groups of life remained relatively
unchanged.
b. Quaternary
Evolution of Humans
Humans evolve from Hominid
primates to Homo Sapien
Whatever the cause, all mass extinctions and existence of new organism resulted in
the adaptive radiation of the species that survived. Adaptive radiation is a process in which
organisms diversify rapidly from an ancestral species into a multitude of new forms,
particularly when a change in the environment makes new resources available, creates new
challenges, or opens new environmental niches. The species that survived a mass
extinction faced much less competition while the new organism in the habitat faced much
more competition. The availability of new niches after mass extinctions probably sparked the
evolution of many species, including primates.
Many times paleontologists will never know exactly how old a fossil is. Usually they
guess its range or span of time. A good way of guessing the range is to look at the layers of
rock that were formed by volcanoes. It's easier to guess the age of volcanic rock because
it's brand new rock from the moment that it is spit onto the earth's surface. "FOSSILS: how
fossils are dated". Retrieved on June 26, 2020 from https://www.youtube.com/watch?v=XR
W-ATOUJus&t=59s
Lesson 2. Mechanisms that Produce Change in Populations
In biology, evolution is the change in the inherited traits of a population from
generation to generation. These traits are the expression of genes that are copied and
passed on to offspring during reproduction. Genetic diversity is always changing — both
across space and through time. Typically, the amount and type of genetic diversity within a
species vary across its natural range. Additionally, its genetic diversity changes over time —
at least in the longterm, and sometimes even over shorter timeframes such as a few
generations of the species. Genetic diversity is affected by several ongoing natural
processes. These processes are: mutation, migration, genetic drift, and selection.

45
Mutation is the origin of all new genetic diversity, occurring when there are
occasional errors in the replication of DNA or other elements of the production and
packaging of genetic information within the cells. Although it implies something negative,
mutations can have positive, neutral, or deleterious impacts. Mutations occur rather slowly
but continuously. Mutations at one level, for example, in the nucleotides that are the basis of
DNA, may not all be expressed at other levels — such as protein differences or observable
changes in the appearance of a plant. The rate of mutation is useful in determining
evolutionary relationships.
Source: https://microbenotes.com/types-of-mutations/
Figure 47. Types of Mutation
Migration is the movement of genetic diversity, usually within a species. In plants,
this occurs through pollen dispersal, seed dispersal, and movement of vegetative
propagules, such as suckers or rhizomes, in species that can reproduce asexually.
Migration, also called gene flow, occurs both with the advancing front of a population when it
is colonizing new areas, and when genes of two or more populations mix through pollen and
seed dispersal. The rate of migration is obviously related to the frequency of reproduction
and the distances over which pollen and seeds typically disperse.
Genetic Drift, or random genetic drift, is simply the change in genetic diversity, or,
more specifically, the change in frequencies of different alleles, over generations because of
chance. For example, every pollen grain contains a different combination of alleles. Which
pollen grains — whether carried by wind, insects, or some other medium — actually succeed
in arriving at a compatible flower and producing a seed — are largely determined by chance
events. Thus, some genetic diversity is usually lost at every generation through these
chance events.
There are two special conditions under which genetic drift occurs.
 Bottleneck effect occurs when a population suddenly gets much smaller. This
might happen because of a natural disaster such as a forest fire. By chance,
allele frequencies of the survivors may be different from those of the original
population.
 Founder effect occurs when a few individuals start, or found, a new
population. By chance, allele frequencies of the founders may be different
from allele frequencies of the population they left.

46
Source: philpoteducation.com/mod/book/tool/print/index.php?id=811&chapterid=1088
Figure 48. Relationship of Bottleneck Effect and Founder Effect
Selection is perhaps the best known of the processes affecting genetic diversity and
is the only process that directly results in populations becoming better adapted to their
environment. For natural selection to occur, there must be differences in fitness and survival
among individuals and a genetic basis for those differences. Over time (generations), those
individuals that are better suited to the environment live, or live longer, and produce more
offspring — those offspring having inherited the more adaptive traits (or rather, have a higher
frequency of the alleles that confer better adaptation).
Source: https://study.com/academy/lesson/genetic-selection-definition-pros-cons.html
Figure 49. Types of Selection
If Evolutionary Forces is Absent
Hardy Weinberg Law states that allele (variant form of a gene e.g B is the dominant
allele for color black cat and b is the recessive allele for color white cat) and genotype
(individual's collection of genes e.g, BB is homozygous dominant for black cat; Bb is
heterozygous dominant for black cat; bb is homozygous recessive for white cat) frequencies
in population will remain constant from generation to generation in the absence of other
evolutionary forces.
Hardy-Weinberg Equilibrium, also referred to as the Hardy-Weinberg principle, is
used to compare allele frequencies in a given population over a period of time. A population
of alleles must meet five rules in order to be considered “in equilibrium”:
1. No gene mutations may occur and therefore allele changes do not occur.
2. There must be no migration of individuals either into or out of the population.
3. Random mating must occur, meaning individuals mate by chance.
4. No genetic drift, a chance change in allele frequency, may occur.
5. No natural selection, a change in allele frequency due to environment, may
occur.
Hardy-Weinberg Equilibrium never occurs in nature because there is always at least
one rule being violated. Hardy-Weinberg Equilibrium is an ideal state that provides a
baseline against which scientists measure gene evolution in a given population. The Hardy-
Weinberg equations can be used for any population; the population does not need to be in
equilibrium.

47
There are two equations necessary to solve a Hardy-Weinberg Equilibrium question:
p is the frequency of the dominant allele.
q is the frequency of the recessive allele.
p2 is the frequency of individuals with the homozygous dominant genotype.
2pq is the frequency of individuals with the heterozygous genotype.
q2 is the frequency of individuals with the homozygous recessive genotype.
Example:
A population of cats can be either black or white; the black allele (B) has complete
dominance over the white allele (b). Given a population of 1,000 cats, 840 black and 160
white, determine the allele frequency, the frequency of individuals per genotype, and
number of individuals per genotype.
To solve this problem, solve for all the preceding variables (p, q, p2, 2pq, q2)
Step 1: Find the frequency of white cats, the homozygous recessive genotype, as
they have only one genotype, bb. Black cats can have either the genotype Bb or the
genotype BB, and therefore, the frequency cannot be directly determined.
Frequency of white cats = 0.16; therefore, q2 = 0.16
Step 2: Find q by taking the square root of q2.
Step 3: Use the first Hardy-Weinberg equation (p + q = 1) to solve for q.
Now that the allele frequencies in the population are known, solve for the remaining
frequency of individuals by using p2 + 2pq + q2 = 1.
Step 4: Square p to find p².
Step 5: Multiply 2 × p × q to get 2pq.
Therefore:

48
The frequency of the dominant alleles: p = 0.6
The frequency of the recessive alleles: q = 0.4
The frequency of individuals with the dominant genotype: p² = 0.36
The frequency of individuals with the heterozygous genotype: 2pq = 0.48
The frequency of individuals with the recessive genotype: q² = 0.16
Remember: Frequencies can be checked by substituting the values above back into the
Hardy-Weinberg equations.
Step 6: Multiply the frequency of individuals (p2, 2pq, and q2) by the total population to get
the number of individuals with that given genotype.
Lesson 3. Development of Evolutionary Thought
In biology, evolution is the change in the characteristics of a species over several
generations and relies on the process of natural selection. The theory of evolution is based
on the idea that all species are related and gradually change over time. Evolution relies on
there being genetic variation in a population which affects the physical characteristics
(phenotype) of an organism. Some of these characteristics may give the individual an
advantage over other individuals which they can then pass on to their offspring. Charles
Darwin’s theory of evolution states that evolution happens by natural selection.
What follows is an attempt to provide that historical setting, with information on the
key players who developed biological and geological thinking and provided the scientific
context about evolution in which Charles Darwin could have his momentous insight.
Table 6. The Historical and Social Context of Darwinism
17th Century: John Ray: the "species" concept
 The first scientist to carry out a thorough study of the
natural world was the Englishman John Ray (1627 -
1705).
 Forced to resign his Fellowship at the university, he was
sponsored by his friend Francis Willughby (1635 -
1672), who shared Ray's scientific interests, to develop
his catalogues of the living world.Ray's particular
interests lay with plants, for which he developed an
early classification system based on physiology and
anatomy. During this work Ray established the concept
of a species, noting that organisms of one species do
not interbreed with members of another, and used it as the basic unit of taxonomy.
 Ray also studied fossils, recognising them as having formed from once-living
organisms, and grappled with the contradictions between the Biblical account of
creation and the evidence of change and extinction that he saw in his fossils.

49
18th Century: Carl Linnaeus & the modern taxonomic
system .
 Ray's ideas on taxonomy were picked up and
extended by the better-known Carl Linnaeus (1707 -
1778).
 He was fascinated by plants, paying botany much
more attention even he is a medical student, and took
up the new idea that plants reproduced sexually, using
differences in reproductive structures to develop a
system for classifying plants.
 He moved on to study animals, and to help make
sense of the huge volume of data accumulated during
his research gave all his specimens a descriptive Latin
binomial, or two-word name.
 The "Systema" built on Ray's earlier work and
catalogued the diversity of living things in a cohesive and logical manner - the now-
familiar hierarchical way of arranging organisms—Classification of Living Things.
 Linnaeus went so far as to include humans in his system, and believed that humans
and the great apes were so closely related that they should be placed in the same
genus. However, he didn't actually do so,to avoid contradicting church teachings.
 Fossils were now well-accepted as the remains of past creatures and he was
uncertain that this distribution could have been achieved in the time provided by the
Biblical flood. Linnaeus with other contemporary scholars of both science and
history were beginning to question the calculations of Archbishop Ussher that gave
the age of the Earth as 6000 years.
Buffon on evolution and the age of the Earth
 A Frenchman Georges Louis Leclerc Comte de Buffon
(1707 - 1788) set out the current knowledge of the
whole of natural history in the 44-volume "Natural
History" ("Histoire Naturelle"), a series that greatly
increased popular interest in science.
 Buffon also gave consideration to the concept of
evolution - a concept that was in circulation long before
Charles Darwin provided a mechanism by which
evolution could occur - wondering about the role of
vestigial organs, which appeared to give the lie to the
idea that creation achieved perfection of form, and
about the possibility of species descending from earlier
(
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50
ancestors.
Erasmus Darwin's thoughts on evolution
 Charles Darwin grandfather is Erasmus Darwin (1731 -
1802) was a successful country doctor who published
widely in many scientific fields.
 He published a book, "The Loves of the Plants"
introduced the public to the intricacies of plant
taxonomy and reproduction and "Zoonomia", set out
Erasmus' ideas on evolution.
 He was aware that modern species were different to
fossil types, and also saw how plant and animal
breeders used artificial selection to enhance their
products.
 He knew that offspring inherited features from their
parents, and he concluded that life on Earth could be descended from a common
ancestor.
 His ideas were not widely accepted in England, but in France Lamarck was
developing similar views of evolutionary change.
Cuvier's contribution to palaeontology
 Georges Cuvier (1769 - 1832) was interested in biology
from childhood, an interest that he developed further
while living in the French countryside during the
Revolution.
 He read both Linnaeus and Buffon and worked on his
own ideas on classification and taxonomy.
 Cuvier also classified animals according to their body
plan (as vertebrates, mollusks, those with jointed
exoskeletons and those with radial symmetry), a major
advance in thinking about relationships.
 His extensive studies of fossils gave rise to the science
of palaeontology, and he recognized that particular
groups of fossil organisms were associated with certain rock strata.
 His palaeontological studies told him that large numbers had become extinct.
 He used the concept of catastrophism: a series of catastrophes, one of which was
recorded in the Biblical story of the flood, had caused repeated waves of extinction.
In his view, life had existed unchanged on Earth for hundreds of thousands of years,
ever since the Creation. Cuvier's adherence to the concept that species were fixed
that he rejected the model of evolution developed by his fellow Frenchman,
Lamarck.

51
Lamarck's concepts of evolution and inheritance
 Jean-Baptiste Lamarck (1744 - 1829) his model of
evolution proposed that individuals were able to pass to
their offspring characteristics acquired during their own
lifetimes.
 Lamarck went further, stating that evolution produced
more complex organisms from simple ancestors, and
that this process of change took time.
 Etienne Geoffroy Saint-Hillaire (1772 - 1844) elaborated
on Lamarck's views. Like Lamarck, he felt that the
environment could produce changes in living things, but
went on to suggest that if these changes were harmful,
then the organism would die; only those well-adapted to
the environment would survive.
 Lamarck's ideas about inheritance of acquired characteristics, were thoroughly
ridiculed by Cuvier.
 And since Cuvier was such a prominent scientist, his attacks carried a lot of weight.
Most scientists accepted the principle of catastrophism that he championed so
strongly, until the work of Englishmen James Hutton and Charles Lyell.
Jean Baptiste Lamarck’s theory on evolutionary change.
Principle of use and disuse
According to Lamarck's theory, a given giraffe could, over a lifetime of straining to
reach high branches, develop an elongated neck. A major downfall of his theory was that he
could not explain how this might happen, though he discussed a "natural tendency toward
perfection."
Another example Lamarck used was the toes of water birds. He proposed that from
years of straining their toes to swim through water, these birds gained elongated, webbed
toes to better their swimming. These two examples demonstrate how use could change a
trait. By the same token, Lamarck believed that disuse would cause a trait to become
reduced. The wings of penguins, for example, would be smaller than those of other birds
because penguins do not use them to fly.
Inheritance of acquired characteristics
He believed that traits changed or acquired over an individual's lifetime could be
passed down to its offspring. Giraffes that had acquired long necks would have offspring
with long necks rather than the short necks their parents were born with. This type of
inheritance, sometimes called Lamarckian inheritance, has since been disproved by the
discovery of hereditary genetics. He studied ancient seashells and noticed that the older
they were, the simpler they appeared. From this, he concluded that species started out
simple and consistently moved toward complexity, or, as he termed it, closer to perfection.

52
Source: http://haw aiireedlab.com/w press/?p=1816
Figure 50. Showing the Elongation of Neck in Giraffe According to Lamarck
Table 7. The Historical and Social Context of Darwinism (continuation)
James Hutton and the principle of uniformitarianism
 James Hutton (1726 - 1797) made a significant contribution
to the understanding of the geological processes that
shaped the Earth.
 He saw that there was no need for global catastrophes to
shape the surface of the Earth. Instead, given sufficient
time, the gradual ongoing processes of erosion,
sedimentation, and uplift could produce the geological
features he saw. This concept became known as the
principle of uniformitarianism.
18th century: Charles Lyell
 Charles Lyell (1797 - 1875) went to Oxford to study
mathematics and law but turned to geology after being
introduced to Hutton's work.
 Lyell travelled widely in Europe, where he observed ancient
raised seabeds separated by lava flows, and became
convinced that Hutton's model of gradual geological change
was correct plus the discovery of Gideon Mantell of several
different dinosaurs.
 He collected a large amount of supporting evidence for
uniformitarianism and set this out in the "Principles of
Geology", a book that had a tremendous influence on Darwin.
 He believe on the idea of gradual long-term natural changes as the shaping force of
the Earth's surface, Lyell considered the origins of plants and animals.
Charles Darwin and the theory of evolution by natural selection
 Charles Robert Darwin (1809 - 1882) was one of six children
born to Robert & Susannah Darwin. Robert was a well-
respected local doctor and also something of a private
investment banker; the family was always very well off.
 Charles was fascinated by science, particularly natural
history, from a young age.
 He graduated from Cambridge University and a letter from
his botany professor, John Henslow, had put his name
forward to join the crew of HMS Beagle, on a surveying
expedition to South America.
 Darwin's thinking was enormously influenced by the work

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