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

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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 or 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
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.


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.