2. 5. Genetics and evolution
• Genetics is a field of biology that studies how traits are
passed from parents to their offspring.
• The passing of traits from parents to offspring is known
as heredity; therefore, genetics is the study of heredity/
inheritance
• Heredity- passing of traits from parent to offspring
• Traits- characteristics that are inherited
Eg. hair color, height, blood type, susceptibility to a
certain disease (diabetes, depression, obesity, breast
cancer)
• The basic components of genetics are DNA, RNA,
genes, chromosomes and genetic inheritance.
• DNA molecules hold all the genetic information for
almost all organisms.
“Father of Genetics”
3. • Five Mendel's conclusions for the establishment of his rules.
– 1. Characters are unitary. That is, they are discrete/individually separated
(purple vs. white, tall vs. dwarf).
– 2. Genetic characteristics have alternate forms, each inherited from one of two
parents. Today, we call these alleles.
– 3. One allele is dominant over the other. The phenotype reflects the dominant
allele.
– 4. Gametes are created by random segregation/separation
• When gametes are formed, the pairs of hereditary factors (genes) become
separated, so that each sex cell (egg/sperm) receives only one kind of gene.
– 5. Different traits have independent assortment. In modern terms, genes are unlinked
– A dominant allele for one trait does not guarantee inheritance of a
dominant allele for a different trait
– genes do not influence each other with regard to the sorting of
alleles into gametes: every possible combination of alleles for every
gene is equally likely to occur.
4. DNA, Gene, Chromosomes and Cell
division
Structure of DNAand chromosome
1.DNA is found in all living things and carries the
instructions to make proteins – A single DNA strand
holds the information to build many different proteins-
molecule that stores genetic information
2.Chromosomes are strands of DNA that are coiled up –
A chromosome holds the information to build many
different proteins
3. Genes are pieces of DNA that hold the information to
build 1 type of protein –Achromosome has many genes
Points to a particular trait/character
5. Structure of DNA
DNA-is made up two
polynucleotides joined
strands of
together and
twisted into a double helix.
The basic unit of DNA strand is a
nucleotide (monomers of DNA).
Sugar-phosphate forms the back bone
Nitrogen bases form the interior,
paired through hydrogen bonds
Forms complementary base pairing
A-T
G-C
Uniform distance between two strands
of the helix
two poly nucleotide chains have anti-
parallel polarity
6. Structure of DNA
• How is DNA helix packed in nucleus?
Prokaryotes:
DNA is organized into loops held by proteins
A region where DNA is present is termed as
Nucleoid
Eukaryotes:
DNA wrap around the histone octamer to form
Nucleosome
Positively charged basic proteins called histone
A nucleosome contains 200 base pairs(bps) of DNA
helix
8. Structure of DNA
Why is DNA a preferred genetic materials?
DNAis structurally and chemically more stable than RNA
DNAhas double stranded structure which provides better ability to rectify errors
during replication
DNAcan not code directly for protein synthesis and thus depend on RNA
10. DNA and RNA
RNA is similar to DNA, but it has three main differences:
11. DNA replication and cell division
Replication: a process of reproducing or creating a copy of something
DNAreplication: It is the process by which DNAmakes a copy of itself during cell
division
Also known as DNASynthesis
DNAstructure is double helix and must replicate semi-conservatively.
– Each formed new DNA molecule contains one strand from the original (old)
DNAand one new strand DNAmolecules.
– Both new DNA molecules formed are identical to each other and to the
original molecule.
12. DNA replication:
Enzymes are involved in this process and the main stages are: DNA Polymerase is the
main enzyme in the replication process.
DNAreplication takes place through the following process
1. DNAhelicase enzyme - break H-bonds to reveal two single strands and unwind (open) the
helix DNA
2. Single stranded binding proteins/SSBP/ stabilize the unwound parental DNA
3. DNApolymerase assembles free DNAnucleotides into new strands alongside each of the
template strands.
– The base sequence in each of these new strands is complementary to its template strand
because of base- pairing rule,A-T, C-G.
4. Two-identical DNAmolecules to each other and the original one is resulted. Each contains
one strand from the original (old) and one newly synthesized.
13. Cell division
Cell division is the process by which a parent cell divides into
two or more daughter cells.
Creates new cells
In eukaryotes, there are two distinct types of cell division:
I. Mitosis:- one cell divides in to two identical diploid
daughter cells.
II.Meiosis: results in four haploid daughter cells by undergoing
one round of DNA replication followed by two divisions.
14.
15. Protein synthesis
Protein synthesis is the process in which a cell makes protein based on
the message contained within its DNA.
RNA (ribonucleic acid) is to carry theses messages from the DNA (in the nucleus)
to the ribosomes (in the cytoplasm)
There are three types of RNA:
1. mRNA – carries a message from the DNA to the cytoplasm
2. tRNA – transports amino acids to the mRNA to make a protein
3. rRNA – make up ribosomes, which make protein.
16. Protein synthesis
Events during protein synthesis are the following:
i. Transcription – DNA - RNA (mRNA) (takes place in
nucleus)
ii. mRNA travels from nucleus to ribosome
iii. Free amino acids are transported from cytoplasm to
ribosome by transfer RNA (tRNA) molecules
iv. Ribosome read mRNA code and assembles amino
acids presented by tRNA into a protein by a process.
It is called translation
19. Codons
There are 20 different amino acids and there are 4 RNA bases
(A,U,G,C).
So how do you exactly go about determining what protein your
cells are going to make?
FIRST, Divide the mRNA sequence into codons.
codon is define as a group of 3 bases specifying a amino acid
Also called world code or triplet code
Since each 3-letter combination “codes” for an amino acid, you
need to figure out what amino acid matches up with each codon:
20. Codons
Since there 4 RNA bases, there are 64 possible triplet codes
the codes of codon is specific
– One codon codes only for 1 an amino acid
Most amino acids have more than one code, only methionine and tryptophan have
one code (Lysine, may code as AAA,AAG)
The genetic code is also a universal code i.e. the triplet code UAU in the DNA code
for amino acid tyrosine in human, redwood tree, bacterium or in any organism E.g.
ACC – threonine, GGG-glycine
There are two types of codons: sense and non-sense codon
Senses codon
– codons which codes for amino acids
– 61 out of 64 are sense codons
Non-sense/stop/ codons
– Codons which are not code for amino acids
– 3 out of 64 are non-sense codons (UAA, UAG, and UGA)
– stop codes signify the end of the coding sequence
22. Mutation
• A mutation is any spontaneous change in the genetic material of
an organism.
• There can be large structural changes involving whole
chromosomes or parts of chromosomes, or changes that involve
only a single base.
• All mutations fall into two basic categories:
• Those that produce changes in a single gene are known as gene
mutations/point mutations.
• Those that produce changes in whole chromosomes are known
as chromosomal mutations.
23. Gene/point mutations
There are several types of point mutation, in which one of the bases in the DNA
sequence of a gene is altered, usually by being copied wrongly when the DNA
replicates.
The different point mutations are: substitution • addition • deletions
Substitutions-In a substitution, one base is changed to a different base.
Substitutions usually affect no more than a single amino acid, and sometimes
they have no effect at all.
24. • Insertions/additions-point mutations in which one base is inserted/added.
• Deletions: are point mutations in which one base is removed from the DNA
sequence.
• If a nucleotide is added or deleted, the bases are still read in groups of three, but
now those groupings shift in every codon that follows the mutation.
Gene/point mutations
25. Chromosomal mutations
Chromosomal mutations involve changes in the number or
structure of chromosomes.
These mutations can change the location of genes on chromosomes
and can even change the number of copies of some genes.
There are four types of chromosomal mutations:
Deletion,
Duplication,
Inversion, And
Translocation.
26. Chromosomal mutations
1. Deletion involves the loss of all
or part of a chromosome.
2. Duplication-produces an extra
copy of all or part of a
chromosome.
3. Inversion-reverses the direction
of parts of a chromosome.
4. Translocation occurs when part
of one chromosome breaks off and
attaches to another
27. ABO blood groups and Rh Factors
ABO Blood Type: An individual's red blood cells will contain proteins of
type A, or B, or both, or neither. The body produces antibodies that will
attack any foreign type.
Alleles of types IA and IB are dominant over type i.
28. • Rh Factor (D antigen): The Rh factor, the second most
important blood group system after the ABO blood group
system, was first discovered in Rhesus monkeys.
– The Rh factor is inherited independently from theABO blood type.
– Genotypes for the Rh factor are +/+, +/-, and -/-.
– People who are +/+ or +/- possess the Rh(D) antigen and test as Rh
positive.
– People who are -/- do not possess the Rh(D) antigen and test as Rh
negative.
29. Rh Sensitization: One interesting medical scenario involves an Rh negative
mother who carries an Rh positive baby.
The baby of an Rh positive father and an Rh negative mother can be +/- or -/-
.)
If the baby is +/-, the first pregnancy causes Rh sensitization in the mother,
because she is exposed to foreign proteins and builds up antibodies against
them.
Future pregnancies can be increasingly difficult, as the mother's antibodies
attack the baby.
30. Introduction to Evolution
Early definition:
Evolution means any changes over a period of time.
It proposes that living things might have evolved from relatively simple chemicals
and explain what happens to organism overtime.
Recent working definition:
Evolution can also be the change in genetic composition of a population over
successive generations which may be caused by meiosis, hybridization, natural
selection or mutation.
This leads to a sequence of events by which the population diverges from other
populations of the same species and may lead to the origin of a new species.
Hence, in evolution there is extinction and new species arise happens.
31.
32. Theories about the origin of life on Earth
Theories about the origin of life on Earth. The theory of evolution
describes how the various forms of life on earth (including humans)
emerged and developed.
There are five main theories of the origin of life on Earth:
Special creationism
Spontaneous generation
Eternity of life
Cosmozoan theory
Biochemical origin
33. 1. Special creationism
Special creation theory states that the different forms of life on
earth were created by a Supreme Being/ God/ at once with six
days.
Special creation is always linked to religion and mainly
focused on that cannot be seen, touched or measured
effectively.
Where as an acceptance of evolution is linked to scientific
thinking.
34. Types of creationism theory
• There are many different versions of special creation, linked to
different religions.
Young earth creationism
Old earth creationism
Day-age and gap creationism
progressive creationism
Theistic evolution/evolutionary
Intelligent design
35. Types of creationism theory
A. Young Earth creationism
This forms of creationism today suggests that the earth
is only a few thousand years old.
This often believe the earth was created in six 24-hours
days.
While they agree that the earth is round and moves
around the sun.
They interpret all geology in the light of Noah’s flood.
36. Types of creationism theory
B. Old earth creationism
They vary in different aspects of how they explain the age
of the earth while still holding to the story found in Genesis.
It accepts that life was created by God as it put in Genesis
but explain that earth is very old.
37. Types of creationism theory
C. Day-age and gap Creationism
Gap creation: discusses a large gap between the
formation of the earth and the creation of all the animals
and plants.
The gap could be billions or millions of year.
Day-age creationism is similar in the length of time but
talks about each of the six days as really meaning a billion
years or so of geologic time; the days are just symbolic.
38. Types of creationism theory
D. Progressive Creationism
This types of creationism accepts the Big Bang as the origin
of the universe.
It accepts the fossil records of a series of creations for all of
the organisms catalogued
However, it does not accept these as part of a continuing
process; each is seen as a unique creation.
Modern species are not seen as being genetically related to
ancient ones.
39. Types of creationism theory
E. Theistic Evolution/ Evolutionary creationism
This view of evolution maintains that God invented
evolution and takes some form of an active part in the
ongoing process of evolution.
It also invokes the role of God in areas not discussed by
science, like the creation of the human soul.
This theory is promoted by the pope for Catholic Church
and is also espoused by most mainline protestants.
40. Types of creationism theory
F. Intelligent Design
This is the newest or latest version of creationism and
maintains that God’s handiwork can be seen in all of creation
if one knows where to look.
It states that life developed due to the combination of natural
force and the intervention of supernatural forces.
The supporter of this theory give sophisticated arguments based
on mathematics and cell biology.
41. 2. Spontaneous generation theory
• Suggests that life can evolve 'spontaneously' from non-living
objects.
• E.g. People believed that rotting meat turned into flies.
• Disproved by the works of Francisco Redi (macro-
organisms) and Louis Pasteur (micro-organisms)
42. 3. Eternity of life
This theory states that the universe has always existed and
that there has always been life in the universe
It had no beginning and end
Life is eternal
Albert Einstein- believed that the universe was unchanging.
43. 4. Cosmozoic Theory (Theory of Panspermia):
Life has reached this planet Earth from other
heavenly bodies such as meteorites, in the form
of highly resistance spores of some organisms.
E.g. Meteorites brought bacterial spores, germs
to the earth.
This idea was proposed by Richter in 1865 and
supported by Arrhenius (1908).
The theory did not gain any support.
This theory lacks evidence, hence it was
discarded.
This theory did not gain any significant support
because it lacks evidence and it is strongly
linked to the „eternity of life‟ theory of the
origin life.
Svante Arrhenius-Swedish
Elise Richter-
Australia
44. 5. Theory of Chemical Evolution:
It suggests that life on earth originated as a result
of a number of biochemical reactions producing
organic molecules, which combined (associated) to
form cells.
Also known as Materialistic Theory or Physico-
chemical Theory.
Oparin and Haldane theory
Origin of life on earth is the result of a slow and
gradual process of chemical evolution that
probably occurred about 3.8 billion years ago.
This theory was proposed independently by two
scientists - A. I. Oparin, a Russian scientist in 1923
and J.B.S Haldane, an English scientist, in 1928.
The entire process of chemical evolution can be
divided in the following steps/ways
Origin of earth and primitive
ATM
Formation of NH4, CO2 and
H2O vapor
Synthesis of simple OCs
Synthesis of complex OCs
Formation of nucleic acids
Formation of 1st cell
Biological evolution
45. In 1953, Stanley Miller/ supervised by Harold
Urey tested the biochemical theory.
He applied electrical sparks repeatedly through
a mixture of gases (NH3, water, H2 and CH4)
that were represent the primitive atmosphere of
the earth (no oxygen) connected a flask of
heated water.
Miller leaving the equipment for
longer periods of time, a larger
variety and more complex
organic molecules were formed
including:
amino acids - to form
proteins
pentose sugar - to form
nucleic acids
hexose sugar - need for
respiration and to form
starch and cellulose.
Hydrogen cyanide (HCN)-
starting point for synthesizes
of nitrogen containing bases
in nucleotides.
This experiment gave strong
evidence to support the Oparin-
Haldane hypothesis
Miller–Urey experiment
46. Theories of Evolution
There have been many theories of evolution that have
explained:- how does evolution happen? And what drives
the population to become a new species?
There are three major theory of evolution
Lamarckism
Darwinism
Neo-Darwinism
47. A. Lamarck Theory of evolution
It was proposed by a French biologist Jean-Baptiste Lamarck at the
beginning of 19th century.
It suggested that the traits acquired by organisms during their
lifetime can pass to the subsequent generation
In the 19th century (1809), Lamarck published a paper entitled
Philosophic „Zoologique‟ in which he described the two-part
mechanism by which change was gradually introduced/changed
(transform) into the species and passed down through the generations.
This theory is also called theory of transformation or Lamarckism.
The two parts of Lamarck theory are:
Use and disuse
Inheritance acquired traits
48. Use and disuse theory:
Lamarck suggested that a structure or process in organism that
can be used continuous will become enlarged or more
developed but any structure that is not.
Little use and disuse of the structure or process leads to the size
reduction or less development
Example, According Lamarck, giraffe had short neck but they
stretched their neck to reach high branches, developed an
elongated neck use theory.
The wings of penguins would have become smaller than those of
other birds because penguins do not use their wings to fly disuse
theory.
49.
50. Inheritance of Acquired traits
Lamarck believed that traits changed (acquired during an organism's
lifetime could be passed on to its offsprings. Example: - Giraffes that
had acquired long necks would have offspring with long necks.
Note: - Nowadays, Lamarck's theories are not accepted because the
environmental changes that were believed by Lamarck have
brought about the changes in the phenotypes (Physical appearance)
of the organisms have no effect on their gametes and hence their
heredity.
Only the genetic changes that occur in the gametes cell can pass to
the offspring
This theory of inheritance of acquired traits was disproved by
genetics.
51. B. Charles Darwin and Natural Selection
In 1858, both Charles Darwin and Alfred Wallace
jointly published a scientific paper that proposed
species were modified by natural selection. Darwin
visited five of the Galapagos Islands, made drawings,
and collected species.
In particular, Darwin studied the finches found on the
different islands and noted there were many
similarities between them but have some obvious
differences.
Darwin concluded that an “ancestral finch” had
colonized the Islands from mainland and been able to
adapt to the different conditions on the islands and
evolve into different species.
E.g. He suggested that some finches had evolved into
insect eaters (pointed peak), other in to seedeaters
(crushing peak)
52. Darwinism theory of natural selection has four core ideas:
Fecundity -all species tend to produce more offspring than can
possibly survive
Variations- there are differences among the offspring
Struggle of the fittest- as there is limited resources and over
reproduced there will be struggle among the offspring for existence.
Survival of the fittest- those member of the species that are better
adapted to the environment will survive.
So, Darwin theory restated/concluded as follow:
Those numbers of the species which are best adapted to their
environment will survive and reproduce in greater numbers than
others less adapted/ died out.
53. C. Neo – Darwinism Theory
A revised version of Darwin’s theory of natural selection.
This theory , now accepted by most biologist, combines Darwin’s
original theory, genetic theory and theories about animal behavior.
Charles Darwin knew very little about genetics and did not propose
how variations in the population was passed to the next generation.
Now days genes and gene action are the driving force of evolution
in the theory of Natural selection.
Genes or, more accurately alleles of genes determine features
a population evolves in to new species when its gene pool is changed
Gene pool refers to all the alleles of all genes in the organisms/
population. Suppose an allele determines a feature that gives an
organism an advantage in its environment.
54. The following will happen
If an allele is advantageous in an organism in a given environment:
The organism survive and reproduce in greater numbers than other
types
They will pass on their advantageous allele in greater numbers to the
offspring of the organism
The frequency of the advantageous allele will be higher in the next
generation of a population.
Mutations are important in introducing variation into population. Any
mutation could produce an allele which:
Confers a selective advantage: the frequency of the allele will increase
over time.
Is neutral in its overall effect: the frequency may increase slowly,
remain stable or decreases (the change in frequency will depend on
what others genes/alleles are associated with the mutant allele
is disadvantageous: the frequency of the allele will be low and could
disappear from the population.
