SlideShare a Scribd company logo
1 of 58
Genetics
General Biology 2 Lesson 1
Genetics
•Branch of science which deals with the study
heredity and variations.
•Heredity – transmission of characteristics
•Variation – differences among the traits
that occur in member of the same species.
Terminologies
Pedigree
This makes use of diagrams
showing the ancestral
relationships and
transmission of genetic
traits over several
generations in a family.
Proband
• The first family member that seeks medical attention.
• The individual in the pedigree that led to the construction of
the pedigree.
Autosomal Trait
• A trait whose alleles that control it are found in the
autosomes (body chromosomes/non-sex
chromosomes).
• Autosomal refers to the 22 numbered chromosomes
as opposed to the sex chromosomes
Genotype
The gene pair an individual carries for a particular trait symbolized with a
pair of letters. By convention, uppercase letter (e.g., A) for a dominant allele
and lowercase letter (e.g., a) for the recessive allele. Any letter in the
alphabet may be used.
For a diploid organism with two alleles in a given gene pair, genotypes may
be written as:
• Homozygous dominant, i.e. with two dominant alleles (DD)
• Heterozygous, i.e. with a dominant and recessive allele (Dd). The
individual will show the dominant phenotype.
• Homozygous recessive, i.e. with two recessive alleles (dd)
Phenotype
The observable trait of an individual based on its genotype.
• Example: red flower, curly hair, blood types (i.e., the blood
type is the phenotype)
For a typical Mendelian trait, phenotypes may either be:
• Dominant. A trait that requires at least one dominant
allele for the trait to be expressed (e.g., Dd)
• Recessive. A trait that requires two recessive alleles for the
trait to be expressed (e.g., dd)
Phenocopy
A trait that is expressed due to specific environmental
conditions (i.e., having hair that is dyed of a different
color) and is not due to the genotype.
Twins
Identical twins. Also known as monozygotic twins, are derived
from a single fertilization event. After the first cleavage or cell
division of the zygote, the cells or blastomeres separate and
become independent blastocysts implanted in the mother’s
uterus.
Fraternal twins. Also known as dizygotic twins, are derived from
separate fertilization events (two eggs fertilized by two sperms)
within the fallopian tube, resulting in two separate zygotes.
Brief History
Gregor Johann Mendel
• He laid the foundation for the formal
discipline of genetics in 1866.
• When Mendel began his studies of
inheritance using the Pea plant (Pisum
sativum), there was no knowledge of
chromosomes or the role and
mechanism of meiosis.
• His work remained unnoticed until
about 1900, following the rediscovery of
his work, the concept of gene as a
hereditary unit was established.
• Even today, they serve as the
cornerstone of the study of Genetics.
Research
Method:
Crossing Pea
Plants
Advantages of pea plants
for genetic study
• There are many varieties with distinct
heritable features or characters (such as
flower color); character variants (such as
purple or white flowers); called traits
• Mating can be controlled
• Each flower has sperm-producing organs
(stamens) and an egg-producing organ (carpel)
• Cross-pollination (fertilization between
different plants) involves dusting one plant
with pollen from another
Mendel’s Experimental Approach
• Mendel chose to track only those characters that
occurred in two distinct alternative forms (such as
purple or white flower color).
• He made sure that he started his experiments with
varieties that were true-breeding (plants that produce
offspring of the same variety when they self-pollinate)
Mendel’s Experimental Approach
• In a typical experiment, Mendel mated two contrasting, true-
breeding varieties, a process called hybridization.
• The true-breeding parents are the P generation (parental
generation).
• The hybrid offspring of the P generation are called the F1
generation
• When F1 individuals self-pollinate or cross- pollinate with other
F1 hybrids, the F2 generation is produced
Laws of Inheritance
Law of Segregation
(First Mendelian Law)
Law of Segregation (First Mendelian Law)
• For every trait governed by a
pair of alleles, these alleles
segregate or separate during
gamete formation in meiosis.
Mendel’s Experiment
• Mendel derived the law of segregation by following a single
character.
• The F1 offspring produced in this cross were monohybrids,
individuals that are heterozygous for one character.
• A cross between such heterozygotes is called a monohybrid
cross.
Mendel’s Experiment
• When Mendel crossed contrasting, true-breeding white- and
purple-flowered pea plants, all of the F1 hybrids were purple.
• When Mendel crossed the F1 hybrids, many of the F2 plants had
purple flowers, but some had white.
• Mendel discovered a ratio of about three to one, purple to
white flowers, in the F2 generation.
P Generation
EXPERIMENT
(true-breeding
parents)
F1 Generation
(hybrids)
F2 Generation
Purple
flowers
White
flowers
All plants had purple flowers
Self- or cross-pollination
705 purple-
flowered
plants
224 white
flowered
plants
Mendel’s Experiment
• Mendel reasoned that only the purple flower factor was
affecting flower color in the F1 hybrids.
• Mendel called the purple flower color a dominant trait and
the white flower color a recessive trait.
• The factor for white flowers was not diluted or destroyed
because it reappeared in the F2 generation.
Mendel’s
Experiment
• Mendel observed
the same pattern
of inheritance in
six other pea
plant characters,
each represented
by two traits.
• What Mendel
called a
“heritable factor”
is what we now
call a gene.
Mendel’s Model
• Mendel developed a hypothesis to explain the 3:1 inheritance
pattern he observed in F2 offspring.
• Four related concepts make up this model
• These concepts can be related to what we now know about
genes and chromosomes
Concept 1: Alternative versions of genes account
for variations in inherited characters
• For example, the gene for flower color in pea plants exists in two
versions, one for purple flowers and the other for white flowers.
• These alternative versions of a gene are called alleles.
Allele for purple flowers
Locus for flower-color gene
Allele for white flowers
Pair of
homologous
chromosomes
Allele - a variant
of the sequence
of nucleotides at
a particular
location (locus)
on a DNA
molecule
Concept 2: For each character, an organism inherits
two alleles, one from each parent
• Mendel made this deduction without knowing about the role of
chromosomes.
• The two alleles at a particular locus may be identical, as in the true-
breeding plants of Mendel’s P generation.
• Alternatively, the two alleles at a locus may differ, as in the F1 hybrids.
Concept 3: If the two alleles at a locus differ, then
one (the dominant allele) determines the
organism’s appearance, and the other (the
recessive allele) has no noticeable effect on
appearance.
• In the flower-color example, the F1 plants had purple flowers
because the allele for that trait is dominant.
Concept 4 (now known as the LAW OF
SEGREGATION): The two alleles for a heritable
character separate (segregate) during gamete
formation and end up in different gametes.
• Thus, an egg or a sperm gets only one of the two alleles that are
present in the organism.
• This segregation of alleles corresponds to the distribution of
homologous chromosomes to different gametes in meiosis.
Useful Genetic Vocabulary
•An organism that has a pair of identical alleles for a gene
encoding a character is called a homozygote and is said to be
homozygous for that gene.
•In the parental generation, the purple-flowered pea plant is
homozygous for the dominant allele (PP), while the white plant
is homozygous for the recessive allele (pp).
•Homozygous plants “breed true” because all of their gametes
contain the same allele—either P or p in this example.
•If we cross dominant homozygotes with recessive homozygotes,
every offspring will have two different alleles—Pp in the case of
the F1 hybrids of our flower color experiment.
Phenotype
Purple
Purple
Purple
White
3
1
1
1
2
Ratio 3:1 Ratio 1:2:1
Genotype
PP
(homozygous)
Pp
(heterozygous)
Pp
(heterozygous)
pp
(homozygous)
•Because of the different effects of dominant and recessive
alleles, an organism’s traits do not always reveal its genetic
composition.
•Therefore, we distinguish between an organism’s appearance or
observable traits, called its phenotype, and its genetic makeup,
its genotype.
•For the case of flower color in pea plants, PP and Pp plants have
the same phenotype (purple flowers) but different genotypes.
•Note that the term phenotype refers to physiological traits as
well as traits that relate directly to appearance.
The Testcross
• How can we tell the genotype of an individual with the
dominant phenotype?
• Such an individual could be either homozygous dominant or
heterozygous.
• The answer is to carry out a testcross: breeding the mystery
individual with a homozygous recessive individual.
• If any offspring display the recessive phenotype, the mystery
parent must be heterozygous.
Dominant phenotype,
unknown genotype:
PP or Pp?
Recessive phenotype,
known genotype:
pp
Predictions
If purple-flowered
parent is PP
If purple-flowered
parent is Pp
or
Sperm Sperm
Eggs Eggs
or
All offspring purple 1/2 offspring purple and
1/2 offspring white
Pp Pp
Pp Pp
Pp Pp
pp pp
p p p p
P
P
P
p
TECHNIQUE
RESULTS
Law of Independent Assortment
(Second Mendelian Law)
Law of Independent Assortment (Second Mendelian
Law)
• A pair of alleles for one trait
will segregate or separate
independently of another pair
of alleles for another trait
during meiosis.
• This law applies only to genes
on different, non-homologous
chromosomes or those far
apart on the same
chromosome.
• Genes located near each other
on the same chromosome tend
to be inherited together.
Mendel’s Experiment
• Mendel identified his second law of inheritance by following
two characters at the same time.
• Crossing two true-breeding parents differing in two characters
produces dihybrids in the F1 generation, heterozygous for both
characters.
• A dihybrid cross, a cross between F1 dihybrids, can determine
whether two characters are transmitted to offspring as a
package or independently.
Mendel’s Experiment
•Imagine crossing two true-breeding pea varieties that differ in both of
these characters—a cross between a plant with yellow-round seeds
(YYRR) and a plant with green-wrinkled seeds (yyrr).
•The F1 plants will be dihybrids, individuals heterozygous for the two
characters being followed in the cross (YyRr).
•But are these two characters transmitted from parents to offspring as a
package?
•That is, will the Y and R alleles always stay together, generation after
generation? Or are seed color and seed shape inherited independently?
•The next figure shows how a dihybrid cross, a cross between F1
dihybrids, can determine which of these two hypotheses is correct.
P Generation
F1 Generation
Predictions
Gametes
EXPERIMENT
RESULTS
YYRR yyrr
yr
YR
YyRr
Hypothesis of
dependent assortment
Hypothesis of
independent assortment
Predicted
offspring of
F2 generation
Sperm
Sperm
or
Eggs
Eggs
Phenotypic ratio 3:1
Phenotypic ratio 9:3:3:1
Phenotypic ratio approximately 9:3:3:1
315 108 101 32
1/2
1/2
1/2
1/2
1/4
1/4
1/4
1/4
1/4
1/4
1/4
1/4
9/16
3/16
3/16
1/16
YR
YR
YR
YR
yr
yr
yr
yr
1/4
3/4
Yr
Yr
yR
yR
YYRR YyRr
YyRr yyrr
YYRR YYRr YyRR YyRr
YYRr YYrr YyRr Yyrr
YyRR YyRr yyRR yyRr
YyRr Yyrr yyRr yyrr
Mendel’s Experiment
• The F1 plants, of genotype YyRr, exhibit both dominant phenotypes,
yellow seeds with round shapes, no matter which hypothesis is correct.
• The key step in the experiment is to see what happens when F1 plants
self-pollinate and produce F2 offspring.
• If the hybrids must transmit their alleles in the same combinations in which
the alleles were inherited from the P generation, then the F1 hybrids will
produce only two classes of gametes: YR and yr.
• As shown on the left side of Figure 14.8, this “dependent assortment”
hypothesis predicts that the phenotypic ratio of the F2 generation will be
3:1, just as in a monohybrid cross:
Mendel’s Experiment
• The alternative hypothesis is that the two pairs of alleles segregate independently of
each other.
• In other words, genes are packaged into gametes in all possible allelic combinations,
as long as each gamete has one allele for each gene.
• In our example, an F1 plant will produce four classes of gametes in equal quantities:
YR, Yr, yR, and yr.
• If sperm of the four classes fertilize eggs of the four classes, there will be 16 (4*4)
equally probable ways in which the alleles can combine in the F2 generation.
• These combinations result in four phenotypic categories with a ratio of 9:3:3:1 (nine
yellow round to three green round to three yellow wrinkled to one green wrinkled):
Mendelian Modes of Inheritance
Monohybrid Cross – one factor cross
• In pea plants, having axial position of flowers on stem
(T) is dominant over the terminal position (t). A
heterozygous axial flower position in a pea plant is
allowed to pollinate by itself.
2. Dihybrid Cross – Two – factor cross
• In pea plants, let us use the same example as in
monohybrid cross (Flower position). Then, let us
combine the traits with yellow and green seed color.
Cross heterozygous axial and yellow with another of the
same kind. Find the phenotypic ratio of the offsprings.
The Laws of Probability Govern Mendelian Inheritance
• Mendel’s laws of segregation and independent
assortment reflect the rules of probability.
• When tossing a coin, the outcome of one toss has no
impact on the outcome of the next toss.
• In the same way, the alleles of one gene segregate into
gametes independently of another gene’s alleles.
• The multiplication rule states that the probability that two or more
independent events will occur together is the product of their
individual probabilities.
• Probability in an F1 monohybrid cross can be determined using the
multiplication rule.
• Segregation in a heterozygous plant is like flipping a coin: Each
gamete has a chance of carrying the dominant allele and a
chance of carrying the recessive allele.
Multiplication Rules Applied to Monohybrid
Crosses
1
2
1
2
We can apply the same reasoning to an F1 monohybrid
cross.
• With seed shape in pea plants as the heritable character, the genotype of F1 plants is Rr.
• Segregation in a heterozygous plant is like flipping a coin in terms of calculating the
probability of each outcome: Each egg produced has a 1⁄2 chance of carrying the dominant
allele (R) and a 1⁄2 chance of carrying the recessive allele (r).
• The same odds apply to each sperm cell produced. For a particular F2 plant to have
wrinkled seeds, the recessive trait, both the egg and the sperm that come together must
carry the r allele.
• The probability that an r allele will be present in both gametes at fertilization is found by
multiplying 1⁄2 (the probability that the egg will have an r) * 1⁄2 (the probability that the
sperm will have an r).
• Thus, the multiplication rule tells us that the probability of an F2 plant having wrinkled
seeds (rr) is 1⁄4. Likewise, the probability of an F2 plant carrying both dominant alleles for
seed shape (RR) is 1⁄4.
Segregation of
alleles into eggs
Segregation of
alleles into sperm
Sperm
Eggs
1/2
1/2
1/2
1/2
1/4
1/4
1/4
1/4
Rr Rr
R
R
R
R
R
R
r
r
r
r r

r
Addition Rule
• The addition rule states that the probability that
any one of two or more exclusive events will
occur is calculated by adding together their
individual probabilities.
• The rule of addition can be used to figure out
the probability that an F2 plant from a
monohybrid cross will be heterozygous rather
than homozygous.
Solving Complex Genetics Problems with the Rules of
Probability
•We can apply the multiplication and addition
rules to predict the outcome of crosses involving
multiple characters.
•A dihybrid or other multi-character cross is
equivalent to two or more independent
monohybrid crosses occurring simultaneously.
•In calculating the chances for various genotypes,
each character is considered separately, and
then the individual probabilities are multiplied.
Probability of YYRR
Probability of YyRR
1/4 (probability of YY)
1/2 (Yy)
1/4 (RR)
1/4 (RR)
1/16
1/8
 




To give two examples, the calculations for finding
the probabilities of two of the possible F2
genotypes (YYRR and YyRR) are shown below:
Seatwork
In tomatoes, two pairs of gene affect the color of the ripe fruit as
follows
R, red flesh; r, yellow flesh; Y, yellow skin; y colorless skin
Dominance is complete for red flesh and yellow skin. If the genes
are independently segregating, calculate the expected
phenotype and genotype ratios from the following crosses:
a. Rryy x rrYy
b. RrYy x rrYy
c. RrYY x Rryy
d. RrYy x RrYy
Solution for Rryy x rrYy
Ry Ry ry ry
rY RrYy RrYy rrYy rrYy
rY RrYy RrYy rrYy rrYy
ry Rryy Rryy rryy rryy
ry Rryy Rryy rryy rryy
Possible combinations for Rrryy = Ry and ry
Possible combinations for rrYy = rY and ry
Probability Probability Probability Probability
RrYy 4/16 = 1/4 Rryy 4/16 = 1/4 rrYy 4/16 = 1/4 rryy 4/16 = 1/4
Another Solution for Rryy x rrYy
R r
r Rr rr
r Rr rr
y y
Y Yy Yy
y yy yy
Probability
RR 0
Rr 2/4 = 1/2
rr 2/4 = 1/2
Probability
YY 0
Yy 2/4 = 1/2
yy 2/4 = 1/2
Combi Probability
RrYy 1/2 (Rr) × 1/2 (Yy) = 1/4
Rryy 1/2 (Rr) × 1/2 (yy) = 1/4
rrYy 1/2 (rr) × 1/2 (Yy) = 1/4
rryy 1/2 (rr) × 1/2 (yy) = 1/4
Phenotypic and Genotypic Ratios for Rryy x rrYy
Combi Prob Phenotype Genotype
RrYy 1/4 Red flesh, yellow skin heterozygous red flesh,
heterozygous yellow skin
Rryy 1/4 Red flesh, colorless skin heterozygous red flesh,
homozygous colorless skin
rrYy 1/4 Yellow flesh, yellow skin homozygous yellow flesh,
heterozygous yellow skin
rryy 1/4 Yellow flesh, colorless skin homozygous yellow flesh,
homozygous colorless skin
Phenotypic ratio = 1:1:1:1
Genotypic ratio = 1:1:1:1
Dominant and Recessive Traits in Humans
Dominant Recessive
Free earlobe Attached ear lobe
Cleft chin No cleft chin
Widow’s peak No widow’s peak
Ability to roll the tongue Inability to roll the tongue
Straight thumb Hitchhiker’s thumb
Arm folding right on top Arm folding left on top
With dimples Without dimples
Dominant and Recessive Traits in Humans
Dominant Recessive
Huntington Disease Alkaptonuria
Marfan Syndrome Color blindness
Congenital night blindness Cystic fibrosis
Neurofibromatosis Muscular dystrophy
Porphyria Hemophilia
Ehler-Danlos Syndrome Sickle-cell anemia
Hypercholesterolemia Tay-Sach’s disease
Achondroplasia Phenylketonuria

More Related Content

Similar to GenBio2 - Lesson 1 - Introduction to Genetics.pptx

Unit 4 genetics and inheritance
Unit 4 genetics and inheritanceUnit 4 genetics and inheritance
Unit 4 genetics and inheritance
Busisiwe Kunene
 
Unit 4 genetics and inheritance
Unit 4 genetics and inheritanceUnit 4 genetics and inheritance
Unit 4 genetics and inheritance
Goodness
 
FBY 0416 - Chapter 4 - Genetic Inheritance (Latest).pptx
FBY 0416 - Chapter 4 - Genetic Inheritance (Latest).pptxFBY 0416 - Chapter 4 - Genetic Inheritance (Latest).pptx
FBY 0416 - Chapter 4 - Genetic Inheritance (Latest).pptx
EuniceTangEnShi
 

Similar to GenBio2 - Lesson 1 - Introduction to Genetics.pptx (20)

genetics and inheritance, in plants and animals
genetics and inheritance, in plants and animalsgenetics and inheritance, in plants and animals
genetics and inheritance, in plants and animals
 
Unit 4 genetics and inheritance
Unit 4 genetics and inheritanceUnit 4 genetics and inheritance
Unit 4 genetics and inheritance
 
Unit 4 genetics and inheritance
Unit 4 genetics and inheritanceUnit 4 genetics and inheritance
Unit 4 genetics and inheritance
 
Life sciences....genetics
Life sciences....geneticsLife sciences....genetics
Life sciences....genetics
 
Unit 4 genetics and inheritance
Unit 4 genetics and inheritanceUnit 4 genetics and inheritance
Unit 4 genetics and inheritance
 
Unit 4 genetics and inheritance
Unit 4 genetics and inheritanceUnit 4 genetics and inheritance
Unit 4 genetics and inheritance
 
Genetics and inheritance
Genetics and inheritanceGenetics and inheritance
Genetics and inheritance
 
Genetics and Inheritance
Genetics and InheritanceGenetics and Inheritance
Genetics and Inheritance
 
Concept_of_genetics_and_Mendel Gregor.pptx
Concept_of_genetics_and_Mendel Gregor.pptxConcept_of_genetics_and_Mendel Gregor.pptx
Concept_of_genetics_and_Mendel Gregor.pptx
 
Genetics FY ppt.pptx
Genetics FY ppt.pptxGenetics FY ppt.pptx
Genetics FY ppt.pptx
 
Principle of Genetics.pptx
Principle of Genetics.pptxPrinciple of Genetics.pptx
Principle of Genetics.pptx
 
General-Biology----------2_Genetics.pptx
General-Biology----------2_Genetics.pptxGeneral-Biology----------2_Genetics.pptx
General-Biology----------2_Genetics.pptx
 
UNIT 4 GENETICS AND INHERITANCE (2).pptx
UNIT 4 GENETICS AND INHERITANCE (2).pptxUNIT 4 GENETICS AND INHERITANCE (2).pptx
UNIT 4 GENETICS AND INHERITANCE (2).pptx
 
genetics and inheritance
genetics and inheritancegenetics and inheritance
genetics and inheritance
 
Genetics - Mendelian2.ppt
Genetics - Mendelian2.pptGenetics - Mendelian2.ppt
Genetics - Mendelian2.ppt
 
Mendel's genetics
Mendel's genetics  Mendel's genetics
Mendel's genetics
 
FBY 0416 - Chapter 4 - Genetic Inheritance (Latest).pptx
FBY 0416 - Chapter 4 - Genetic Inheritance (Latest).pptxFBY 0416 - Chapter 4 - Genetic Inheritance (Latest).pptx
FBY 0416 - Chapter 4 - Genetic Inheritance (Latest).pptx
 
Genetics Powerpoint.pptx
Genetics Powerpoint.pptxGenetics Powerpoint.pptx
Genetics Powerpoint.pptx
 
Mendel’s genetics
Mendel’s geneticsMendel’s genetics
Mendel’s genetics
 
Mendellism
MendellismMendellism
Mendellism
 

More from BerniceCayabyab1 (11)

Chapter 3.2 - Human Rights and the Grassroots.pptx
Chapter 3.2 - Human Rights and the Grassroots.pptxChapter 3.2 - Human Rights and the Grassroots.pptx
Chapter 3.2 - Human Rights and the Grassroots.pptx
 
Writing A Research Title
Writing A Research TitleWriting A Research Title
Writing A Research Title
 
Psychoanalysis.pptx
Psychoanalysis.pptxPsychoanalysis.pptx
Psychoanalysis.pptx
 
Q2 LESSON 3 HUMAN ACTIVITIES AND ENVIRONMENT.pdf
Q2 LESSON 3 HUMAN ACTIVITIES AND ENVIRONMENT.pdfQ2 LESSON 3 HUMAN ACTIVITIES AND ENVIRONMENT.pdf
Q2 LESSON 3 HUMAN ACTIVITIES AND ENVIRONMENT.pdf
 
Q2 LESSON 2 SOIL AND SOIL QUALITY.pptx
Q2 LESSON 2 SOIL AND SOIL QUALITY.pptxQ2 LESSON 2 SOIL AND SOIL QUALITY.pptx
Q2 LESSON 2 SOIL AND SOIL QUALITY.pptx
 
DEFENSE-MECHANISM.pptx
DEFENSE-MECHANISM.pptxDEFENSE-MECHANISM.pptx
DEFENSE-MECHANISM.pptx
 
Water Resources.pptx
Water Resources.pptxWater Resources.pptx
Water Resources.pptx
 
Lesson 12 Energy Resources - Hydrothermal, Solar, and Wind Energy.pptx
Lesson 12 Energy Resources - Hydrothermal, Solar, and Wind Energy.pptxLesson 12 Energy Resources - Hydrothermal, Solar, and Wind Energy.pptx
Lesson 12 Energy Resources - Hydrothermal, Solar, and Wind Energy.pptx
 
Lesson 7 Earth and Earth Resources - Mineral Resources.pptx
Lesson 7 Earth and Earth Resources - Mineral Resources.pptxLesson 7 Earth and Earth Resources - Mineral Resources.pptx
Lesson 7 Earth and Earth Resources - Mineral Resources.pptx
 
Earth Subsystems
Earth SubsystemsEarth Subsystems
Earth Subsystems
 
Characteristics of Earth that Sustain Life.pptx
Characteristics of Earth that Sustain Life.pptxCharacteristics of Earth that Sustain Life.pptx
Characteristics of Earth that Sustain Life.pptx
 

Recently uploaded

Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...
Sérgio Sacani
 
The importance of continents, oceans and plate tectonics for the evolution of...
The importance of continents, oceans and plate tectonics for the evolution of...The importance of continents, oceans and plate tectonics for the evolution of...
The importance of continents, oceans and plate tectonics for the evolution of...
Sérgio Sacani
 
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...
Sérgio Sacani
 
Continuum emission from within the plunging region of black hole discs
Continuum emission from within the plunging region of black hole discsContinuum emission from within the plunging region of black hole discs
Continuum emission from within the plunging region of black hole discs
Sérgio Sacani
 
Climate extremes likely to drive land mammal extinction during next supercont...
Climate extremes likely to drive land mammal extinction during next supercont...Climate extremes likely to drive land mammal extinction during next supercont...
Climate extremes likely to drive land mammal extinction during next supercont...
Sérgio Sacani
 
Quantifying Artificial Intelligence and What Comes Next!
Quantifying Artificial Intelligence and What Comes Next!Quantifying Artificial Intelligence and What Comes Next!
Quantifying Artificial Intelligence and What Comes Next!
University of Hertfordshire
 

Recently uploaded (20)

Cell Immobilization Methods and Applications.pptx
Cell Immobilization Methods and Applications.pptxCell Immobilization Methods and Applications.pptx
Cell Immobilization Methods and Applications.pptx
 
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...
 
The importance of continents, oceans and plate tectonics for the evolution of...
The importance of continents, oceans and plate tectonics for the evolution of...The importance of continents, oceans and plate tectonics for the evolution of...
The importance of continents, oceans and plate tectonics for the evolution of...
 
KOCH'S POSTULATE: an extensive over view.pptx
KOCH'S POSTULATE: an extensive over view.pptxKOCH'S POSTULATE: an extensive over view.pptx
KOCH'S POSTULATE: an extensive over view.pptx
 
Plasmapheresis - Dr. E. Muralinath - Kalyan . C.pptx
Plasmapheresis - Dr. E. Muralinath - Kalyan . C.pptxPlasmapheresis - Dr. E. Muralinath - Kalyan . C.pptx
Plasmapheresis - Dr. E. Muralinath - Kalyan . C.pptx
 
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...
 
INSIGHT Partner Profile: Tampere University
INSIGHT Partner Profile: Tampere UniversityINSIGHT Partner Profile: Tampere University
INSIGHT Partner Profile: Tampere University
 
GBSN - Microbiology (Unit 6) Human and Microbial interaction
GBSN - Microbiology (Unit 6) Human and Microbial interactionGBSN - Microbiology (Unit 6) Human and Microbial interaction
GBSN - Microbiology (Unit 6) Human and Microbial interaction
 
Topography and sediments of the floor of the Bay of Bengal
Topography and sediments of the floor of the Bay of BengalTopography and sediments of the floor of the Bay of Bengal
Topography and sediments of the floor of the Bay of Bengal
 
The Scientific names of some important families of Industrial plants .pdf
The Scientific names of some important families of Industrial plants .pdfThe Scientific names of some important families of Industrial plants .pdf
The Scientific names of some important families of Industrial plants .pdf
 
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...
 
PLANT DISEASE MANAGEMENT PRINCIPLES AND ITS IMPORTANCE
PLANT DISEASE MANAGEMENT PRINCIPLES AND ITS IMPORTANCEPLANT DISEASE MANAGEMENT PRINCIPLES AND ITS IMPORTANCE
PLANT DISEASE MANAGEMENT PRINCIPLES AND ITS IMPORTANCE
 
Ostiguy & Panizza & Moffitt (eds.) - Populism in Global Perspective. A Perfor...
Ostiguy & Panizza & Moffitt (eds.) - Populism in Global Perspective. A Perfor...Ostiguy & Panizza & Moffitt (eds.) - Populism in Global Perspective. A Perfor...
Ostiguy & Panizza & Moffitt (eds.) - Populism in Global Perspective. A Perfor...
 
Continuum emission from within the plunging region of black hole discs
Continuum emission from within the plunging region of black hole discsContinuum emission from within the plunging region of black hole discs
Continuum emission from within the plunging region of black hole discs
 
Climate extremes likely to drive land mammal extinction during next supercont...
Climate extremes likely to drive land mammal extinction during next supercont...Climate extremes likely to drive land mammal extinction during next supercont...
Climate extremes likely to drive land mammal extinction during next supercont...
 
Quantifying Artificial Intelligence and What Comes Next!
Quantifying Artificial Intelligence and What Comes Next!Quantifying Artificial Intelligence and What Comes Next!
Quantifying Artificial Intelligence and What Comes Next!
 
GBSN - Microbiology Lab 2 (Compound Microscope)
GBSN - Microbiology Lab 2 (Compound Microscope)GBSN - Microbiology Lab 2 (Compound Microscope)
GBSN - Microbiology Lab 2 (Compound Microscope)
 
word2vec, node2vec, graph2vec, X2vec: Towards a Theory of Vector Embeddings o...
word2vec, node2vec, graph2vec, X2vec: Towards a Theory of Vector Embeddings o...word2vec, node2vec, graph2vec, X2vec: Towards a Theory of Vector Embeddings o...
word2vec, node2vec, graph2vec, X2vec: Towards a Theory of Vector Embeddings o...
 
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243
 
NuGOweek 2024 full programme - hosted by Ghent University
NuGOweek 2024 full programme - hosted by Ghent UniversityNuGOweek 2024 full programme - hosted by Ghent University
NuGOweek 2024 full programme - hosted by Ghent University
 

GenBio2 - Lesson 1 - Introduction to Genetics.pptx

  • 2. Genetics •Branch of science which deals with the study heredity and variations. •Heredity – transmission of characteristics •Variation – differences among the traits that occur in member of the same species.
  • 4. Pedigree This makes use of diagrams showing the ancestral relationships and transmission of genetic traits over several generations in a family.
  • 5. Proband • The first family member that seeks medical attention. • The individual in the pedigree that led to the construction of the pedigree.
  • 6. Autosomal Trait • A trait whose alleles that control it are found in the autosomes (body chromosomes/non-sex chromosomes). • Autosomal refers to the 22 numbered chromosomes as opposed to the sex chromosomes
  • 7. Genotype The gene pair an individual carries for a particular trait symbolized with a pair of letters. By convention, uppercase letter (e.g., A) for a dominant allele and lowercase letter (e.g., a) for the recessive allele. Any letter in the alphabet may be used. For a diploid organism with two alleles in a given gene pair, genotypes may be written as: • Homozygous dominant, i.e. with two dominant alleles (DD) • Heterozygous, i.e. with a dominant and recessive allele (Dd). The individual will show the dominant phenotype. • Homozygous recessive, i.e. with two recessive alleles (dd)
  • 8. Phenotype The observable trait of an individual based on its genotype. • Example: red flower, curly hair, blood types (i.e., the blood type is the phenotype) For a typical Mendelian trait, phenotypes may either be: • Dominant. A trait that requires at least one dominant allele for the trait to be expressed (e.g., Dd) • Recessive. A trait that requires two recessive alleles for the trait to be expressed (e.g., dd)
  • 9. Phenocopy A trait that is expressed due to specific environmental conditions (i.e., having hair that is dyed of a different color) and is not due to the genotype.
  • 10. Twins Identical twins. Also known as monozygotic twins, are derived from a single fertilization event. After the first cleavage or cell division of the zygote, the cells or blastomeres separate and become independent blastocysts implanted in the mother’s uterus. Fraternal twins. Also known as dizygotic twins, are derived from separate fertilization events (two eggs fertilized by two sperms) within the fallopian tube, resulting in two separate zygotes.
  • 12. Gregor Johann Mendel • He laid the foundation for the formal discipline of genetics in 1866. • When Mendel began his studies of inheritance using the Pea plant (Pisum sativum), there was no knowledge of chromosomes or the role and mechanism of meiosis. • His work remained unnoticed until about 1900, following the rediscovery of his work, the concept of gene as a hereditary unit was established. • Even today, they serve as the cornerstone of the study of Genetics.
  • 14. Advantages of pea plants for genetic study • There are many varieties with distinct heritable features or characters (such as flower color); character variants (such as purple or white flowers); called traits • Mating can be controlled • Each flower has sperm-producing organs (stamens) and an egg-producing organ (carpel) • Cross-pollination (fertilization between different plants) involves dusting one plant with pollen from another
  • 15. Mendel’s Experimental Approach • Mendel chose to track only those characters that occurred in two distinct alternative forms (such as purple or white flower color). • He made sure that he started his experiments with varieties that were true-breeding (plants that produce offspring of the same variety when they self-pollinate)
  • 16. Mendel’s Experimental Approach • In a typical experiment, Mendel mated two contrasting, true- breeding varieties, a process called hybridization. • The true-breeding parents are the P generation (parental generation). • The hybrid offspring of the P generation are called the F1 generation • When F1 individuals self-pollinate or cross- pollinate with other F1 hybrids, the F2 generation is produced
  • 18.
  • 19. Law of Segregation (First Mendelian Law)
  • 20. Law of Segregation (First Mendelian Law) • For every trait governed by a pair of alleles, these alleles segregate or separate during gamete formation in meiosis.
  • 21. Mendel’s Experiment • Mendel derived the law of segregation by following a single character. • The F1 offspring produced in this cross were monohybrids, individuals that are heterozygous for one character. • A cross between such heterozygotes is called a monohybrid cross.
  • 22. Mendel’s Experiment • When Mendel crossed contrasting, true-breeding white- and purple-flowered pea plants, all of the F1 hybrids were purple. • When Mendel crossed the F1 hybrids, many of the F2 plants had purple flowers, but some had white. • Mendel discovered a ratio of about three to one, purple to white flowers, in the F2 generation.
  • 23. P Generation EXPERIMENT (true-breeding parents) F1 Generation (hybrids) F2 Generation Purple flowers White flowers All plants had purple flowers Self- or cross-pollination 705 purple- flowered plants 224 white flowered plants
  • 24. Mendel’s Experiment • Mendel reasoned that only the purple flower factor was affecting flower color in the F1 hybrids. • Mendel called the purple flower color a dominant trait and the white flower color a recessive trait. • The factor for white flowers was not diluted or destroyed because it reappeared in the F2 generation.
  • 25. Mendel’s Experiment • Mendel observed the same pattern of inheritance in six other pea plant characters, each represented by two traits. • What Mendel called a “heritable factor” is what we now call a gene.
  • 26. Mendel’s Model • Mendel developed a hypothesis to explain the 3:1 inheritance pattern he observed in F2 offspring. • Four related concepts make up this model • These concepts can be related to what we now know about genes and chromosomes
  • 27. Concept 1: Alternative versions of genes account for variations in inherited characters • For example, the gene for flower color in pea plants exists in two versions, one for purple flowers and the other for white flowers. • These alternative versions of a gene are called alleles. Allele for purple flowers Locus for flower-color gene Allele for white flowers Pair of homologous chromosomes Allele - a variant of the sequence of nucleotides at a particular location (locus) on a DNA molecule
  • 28. Concept 2: For each character, an organism inherits two alleles, one from each parent • Mendel made this deduction without knowing about the role of chromosomes. • The two alleles at a particular locus may be identical, as in the true- breeding plants of Mendel’s P generation. • Alternatively, the two alleles at a locus may differ, as in the F1 hybrids.
  • 29. Concept 3: If the two alleles at a locus differ, then one (the dominant allele) determines the organism’s appearance, and the other (the recessive allele) has no noticeable effect on appearance. • In the flower-color example, the F1 plants had purple flowers because the allele for that trait is dominant.
  • 30. Concept 4 (now known as the LAW OF SEGREGATION): The two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes. • Thus, an egg or a sperm gets only one of the two alleles that are present in the organism. • This segregation of alleles corresponds to the distribution of homologous chromosomes to different gametes in meiosis.
  • 31. Useful Genetic Vocabulary •An organism that has a pair of identical alleles for a gene encoding a character is called a homozygote and is said to be homozygous for that gene. •In the parental generation, the purple-flowered pea plant is homozygous for the dominant allele (PP), while the white plant is homozygous for the recessive allele (pp). •Homozygous plants “breed true” because all of their gametes contain the same allele—either P or p in this example. •If we cross dominant homozygotes with recessive homozygotes, every offspring will have two different alleles—Pp in the case of the F1 hybrids of our flower color experiment.
  • 32. Phenotype Purple Purple Purple White 3 1 1 1 2 Ratio 3:1 Ratio 1:2:1 Genotype PP (homozygous) Pp (heterozygous) Pp (heterozygous) pp (homozygous)
  • 33. •Because of the different effects of dominant and recessive alleles, an organism’s traits do not always reveal its genetic composition. •Therefore, we distinguish between an organism’s appearance or observable traits, called its phenotype, and its genetic makeup, its genotype. •For the case of flower color in pea plants, PP and Pp plants have the same phenotype (purple flowers) but different genotypes. •Note that the term phenotype refers to physiological traits as well as traits that relate directly to appearance.
  • 34. The Testcross • How can we tell the genotype of an individual with the dominant phenotype? • Such an individual could be either homozygous dominant or heterozygous. • The answer is to carry out a testcross: breeding the mystery individual with a homozygous recessive individual. • If any offspring display the recessive phenotype, the mystery parent must be heterozygous.
  • 35. Dominant phenotype, unknown genotype: PP or Pp? Recessive phenotype, known genotype: pp Predictions If purple-flowered parent is PP If purple-flowered parent is Pp or Sperm Sperm Eggs Eggs or All offspring purple 1/2 offspring purple and 1/2 offspring white Pp Pp Pp Pp Pp Pp pp pp p p p p P P P p TECHNIQUE RESULTS
  • 36. Law of Independent Assortment (Second Mendelian Law)
  • 37. Law of Independent Assortment (Second Mendelian Law) • A pair of alleles for one trait will segregate or separate independently of another pair of alleles for another trait during meiosis. • This law applies only to genes on different, non-homologous chromosomes or those far apart on the same chromosome. • Genes located near each other on the same chromosome tend to be inherited together.
  • 38. Mendel’s Experiment • Mendel identified his second law of inheritance by following two characters at the same time. • Crossing two true-breeding parents differing in two characters produces dihybrids in the F1 generation, heterozygous for both characters. • A dihybrid cross, a cross between F1 dihybrids, can determine whether two characters are transmitted to offspring as a package or independently.
  • 39. Mendel’s Experiment •Imagine crossing two true-breeding pea varieties that differ in both of these characters—a cross between a plant with yellow-round seeds (YYRR) and a plant with green-wrinkled seeds (yyrr). •The F1 plants will be dihybrids, individuals heterozygous for the two characters being followed in the cross (YyRr). •But are these two characters transmitted from parents to offspring as a package? •That is, will the Y and R alleles always stay together, generation after generation? Or are seed color and seed shape inherited independently? •The next figure shows how a dihybrid cross, a cross between F1 dihybrids, can determine which of these two hypotheses is correct.
  • 40. P Generation F1 Generation Predictions Gametes EXPERIMENT RESULTS YYRR yyrr yr YR YyRr Hypothesis of dependent assortment Hypothesis of independent assortment Predicted offspring of F2 generation Sperm Sperm or Eggs Eggs Phenotypic ratio 3:1 Phenotypic ratio 9:3:3:1 Phenotypic ratio approximately 9:3:3:1 315 108 101 32 1/2 1/2 1/2 1/2 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 9/16 3/16 3/16 1/16 YR YR YR YR yr yr yr yr 1/4 3/4 Yr Yr yR yR YYRR YyRr YyRr yyrr YYRR YYRr YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr Yyrr yyRr yyrr
  • 41. Mendel’s Experiment • The F1 plants, of genotype YyRr, exhibit both dominant phenotypes, yellow seeds with round shapes, no matter which hypothesis is correct. • The key step in the experiment is to see what happens when F1 plants self-pollinate and produce F2 offspring. • If the hybrids must transmit their alleles in the same combinations in which the alleles were inherited from the P generation, then the F1 hybrids will produce only two classes of gametes: YR and yr. • As shown on the left side of Figure 14.8, this “dependent assortment” hypothesis predicts that the phenotypic ratio of the F2 generation will be 3:1, just as in a monohybrid cross:
  • 42. Mendel’s Experiment • The alternative hypothesis is that the two pairs of alleles segregate independently of each other. • In other words, genes are packaged into gametes in all possible allelic combinations, as long as each gamete has one allele for each gene. • In our example, an F1 plant will produce four classes of gametes in equal quantities: YR, Yr, yR, and yr. • If sperm of the four classes fertilize eggs of the four classes, there will be 16 (4*4) equally probable ways in which the alleles can combine in the F2 generation. • These combinations result in four phenotypic categories with a ratio of 9:3:3:1 (nine yellow round to three green round to three yellow wrinkled to one green wrinkled):
  • 43. Mendelian Modes of Inheritance
  • 44. Monohybrid Cross – one factor cross • In pea plants, having axial position of flowers on stem (T) is dominant over the terminal position (t). A heterozygous axial flower position in a pea plant is allowed to pollinate by itself.
  • 45. 2. Dihybrid Cross – Two – factor cross • In pea plants, let us use the same example as in monohybrid cross (Flower position). Then, let us combine the traits with yellow and green seed color. Cross heterozygous axial and yellow with another of the same kind. Find the phenotypic ratio of the offsprings.
  • 46. The Laws of Probability Govern Mendelian Inheritance • Mendel’s laws of segregation and independent assortment reflect the rules of probability. • When tossing a coin, the outcome of one toss has no impact on the outcome of the next toss. • In the same way, the alleles of one gene segregate into gametes independently of another gene’s alleles.
  • 47. • The multiplication rule states that the probability that two or more independent events will occur together is the product of their individual probabilities. • Probability in an F1 monohybrid cross can be determined using the multiplication rule. • Segregation in a heterozygous plant is like flipping a coin: Each gamete has a chance of carrying the dominant allele and a chance of carrying the recessive allele. Multiplication Rules Applied to Monohybrid Crosses 1 2 1 2
  • 48. We can apply the same reasoning to an F1 monohybrid cross. • With seed shape in pea plants as the heritable character, the genotype of F1 plants is Rr. • Segregation in a heterozygous plant is like flipping a coin in terms of calculating the probability of each outcome: Each egg produced has a 1⁄2 chance of carrying the dominant allele (R) and a 1⁄2 chance of carrying the recessive allele (r). • The same odds apply to each sperm cell produced. For a particular F2 plant to have wrinkled seeds, the recessive trait, both the egg and the sperm that come together must carry the r allele. • The probability that an r allele will be present in both gametes at fertilization is found by multiplying 1⁄2 (the probability that the egg will have an r) * 1⁄2 (the probability that the sperm will have an r). • Thus, the multiplication rule tells us that the probability of an F2 plant having wrinkled seeds (rr) is 1⁄4. Likewise, the probability of an F2 plant carrying both dominant alleles for seed shape (RR) is 1⁄4.
  • 49. Segregation of alleles into eggs Segregation of alleles into sperm Sperm Eggs 1/2 1/2 1/2 1/2 1/4 1/4 1/4 1/4 Rr Rr R R R R R R r r r r r  r
  • 50. Addition Rule • The addition rule states that the probability that any one of two or more exclusive events will occur is calculated by adding together their individual probabilities. • The rule of addition can be used to figure out the probability that an F2 plant from a monohybrid cross will be heterozygous rather than homozygous.
  • 51. Solving Complex Genetics Problems with the Rules of Probability •We can apply the multiplication and addition rules to predict the outcome of crosses involving multiple characters. •A dihybrid or other multi-character cross is equivalent to two or more independent monohybrid crosses occurring simultaneously. •In calculating the chances for various genotypes, each character is considered separately, and then the individual probabilities are multiplied.
  • 52. Probability of YYRR Probability of YyRR 1/4 (probability of YY) 1/2 (Yy) 1/4 (RR) 1/4 (RR) 1/16 1/8       To give two examples, the calculations for finding the probabilities of two of the possible F2 genotypes (YYRR and YyRR) are shown below:
  • 53. Seatwork In tomatoes, two pairs of gene affect the color of the ripe fruit as follows R, red flesh; r, yellow flesh; Y, yellow skin; y colorless skin Dominance is complete for red flesh and yellow skin. If the genes are independently segregating, calculate the expected phenotype and genotype ratios from the following crosses: a. Rryy x rrYy b. RrYy x rrYy c. RrYY x Rryy d. RrYy x RrYy
  • 54. Solution for Rryy x rrYy Ry Ry ry ry rY RrYy RrYy rrYy rrYy rY RrYy RrYy rrYy rrYy ry Rryy Rryy rryy rryy ry Rryy Rryy rryy rryy Possible combinations for Rrryy = Ry and ry Possible combinations for rrYy = rY and ry Probability Probability Probability Probability RrYy 4/16 = 1/4 Rryy 4/16 = 1/4 rrYy 4/16 = 1/4 rryy 4/16 = 1/4
  • 55. Another Solution for Rryy x rrYy R r r Rr rr r Rr rr y y Y Yy Yy y yy yy Probability RR 0 Rr 2/4 = 1/2 rr 2/4 = 1/2 Probability YY 0 Yy 2/4 = 1/2 yy 2/4 = 1/2 Combi Probability RrYy 1/2 (Rr) × 1/2 (Yy) = 1/4 Rryy 1/2 (Rr) × 1/2 (yy) = 1/4 rrYy 1/2 (rr) × 1/2 (Yy) = 1/4 rryy 1/2 (rr) × 1/2 (yy) = 1/4
  • 56. Phenotypic and Genotypic Ratios for Rryy x rrYy Combi Prob Phenotype Genotype RrYy 1/4 Red flesh, yellow skin heterozygous red flesh, heterozygous yellow skin Rryy 1/4 Red flesh, colorless skin heterozygous red flesh, homozygous colorless skin rrYy 1/4 Yellow flesh, yellow skin homozygous yellow flesh, heterozygous yellow skin rryy 1/4 Yellow flesh, colorless skin homozygous yellow flesh, homozygous colorless skin Phenotypic ratio = 1:1:1:1 Genotypic ratio = 1:1:1:1
  • 57. Dominant and Recessive Traits in Humans Dominant Recessive Free earlobe Attached ear lobe Cleft chin No cleft chin Widow’s peak No widow’s peak Ability to roll the tongue Inability to roll the tongue Straight thumb Hitchhiker’s thumb Arm folding right on top Arm folding left on top With dimples Without dimples
  • 58. Dominant and Recessive Traits in Humans Dominant Recessive Huntington Disease Alkaptonuria Marfan Syndrome Color blindness Congenital night blindness Cystic fibrosis Neurofibromatosis Muscular dystrophy Porphyria Hemophilia Ehler-Danlos Syndrome Sickle-cell anemia Hypercholesterolemia Tay-Sach’s disease Achondroplasia Phenylketonuria