Transcript 11-3 Exploring Mendelian Genetics


Independent Assortment- Genes that
segregate (separately) independently do not
influence each other's inheritance.

The principle of independent assortment states
that genes for different traits can segregate
independently during the formation of gametes.

Mendel did a two-factor (trait) cross to see if
the separation of one pair of alleles affects
the separation of another pair of alleles.
 Instead of crossing a yellow seed with a green
seed; he observed seed color and seed shape
together

Seeds that are round (R) and yellow (Y) are
dominant to seeds that are wrinkled (r) &
green (y)
True-breeding round & yellow (RRYY)seeds
were crossed with true breeding wrinkled and
green seeds (rryy)
 The result: All individuals in the F1 generation
were round & yellow

The Two Factor Cross: F2

Heterozygous F1 plants (RrYy) were crossed
with each other to determine if the alleles would
segregate from each other in the F2 generation.
RrYy × RrYy
The Punnett square predicts a 9 : 3 : 3 :1 ratio
in the F2 generation
 9 round & yellow: 3 round & green: 3 wrinkled
& yellow: 1 wrinkled & green


The results of the experiment:
 some seeds were round and yellow
 some seeds were wrinkled and green
 some seeds were round and green
 some seeds were wrinkled and yellow


Mendel had discovered the principle of
independent assortment
Independent Assortment explains the
variation observed in plants, animals,
and other organisms
A Summary of Mendel's
Principles
Genes are passed from parents to their
offspring.
 If there are two or more alleles for a gene,
some of the alleles may be dominant and
others may be recessive.
 In most sexually reproducing organisms, each
adult has two copies of each gene. These
genes are segregated from each other when
gametes are formed.
 The alleles for different genes usually
segregate independently of one another


Not all traits are dominant or recessive

Some traits are controlled by more than
one gene or many alleles
Incomplete Dominance


One allele is not
completely dominant
over the other
The heterozygous
phenotype is b/w the
two homozygous
phenotypes
A cross between red (RR) and white
(WW) four o’clock plants produces
pink-colored flowers (RW).
Codominance both
alleles
contribute to
the phenotype.

Heterozygous chickens are
speckled with both black and
white feathers. The black and
white colors do not blend to
form a new color, but appear
separately.
Multiple Alleles
Genes that are controlled by more than
two alleles

more than two possible alleles can exist
in a population
Coat color in rabbits is determined by a
single gene that has at least four different
alleles.
C = full color; dominant to
all other alleles
 cch
= chinchilla; partial
defect in pigmentation;
dominant to ch and c alleles
 ch
= Himalayan; color in certain parts of
the body; dominant to c allele

c = albino; no color; recessive to all other
alleles
Polygenic Traits Traits
controlled
by two or more
genes

Skin, hair, & eye
color in humans
are polygenic traits
controlled by more
than four different
genes
This couples daughters have traits that
are similar but not exactly like


Thomas Hunt
Morgan used fruit
flies to advance the
study of genetics
Morgan and scientist
tested Mendel’s
principles and
learned that they
applied to other
organisms as well
as plants.
Fruit flies with their food in test tubes
An Indian family

Mendel’s principles
can be used to
study inheritance of
human traits and to
calculate the
probability of certain
traits appearing in
the next generation

Characteristics of
any organism are
determined by the
interaction between
genes and the
environment.
 Ex: an individual has
the gene to develop
type 2 diabetes but
their diet
(environment) will
determine if the will
have it.
Eating high calorie foods and no exercise can result in
obesity