Download Non-Mendelian Inheritance

Why are only female cats calico?
 This
is when both genes
are dominant, so the
presence of both alleles
you will see they are
both fully expressed.
 IA I A
or IAi= A type
A
B
I I = AB type
IBIB or IBi = B type
ii = O type

Neither of the genes is dominant to the other, so the
heterozygous genotype creates a 3rd phenotype.

The two phenotypes are blended.
Roan Horse

Which is an
example of
incomplete
dominance and
which is an
example of
codominance?

Most traits in humans are not controlled
by only 1 gene. There are many genes
that contribute to a single trait.
Eye color
Hair color
•
A modifier gene controls another gene.
•
Not dominant, because it is not on the same
gene, but will still override whatever gene it
is the modifier for.
Heterochromia iridum
Eye color is an example of a polygenic trait
and Albinism is an example of a blocked trait.
 How
 How
is eye color determined?
is whether or not an organism will be
albino determined?

Some traits are carried on the sex chromosomes.
Women have XX and men have XY.

If a trait is carried on the X chromosome then
women have two of them and men only have
one.
hemophilia
Muscular dystrophy
An
example of this is color
blindness
Ex: Red/green color blindness is a
recessive trait carried on the X
chromosome.

Men can have either XBY or XbY

If he has XBY he is not color blind (the big B
stands for the dominant trait of not color
blind)

If he has XbY he is colorblind.

Because this trait is not carried on the Y
chromosome there is no opportunity to be
heterozygous for males.
 Women
 If
can have XBXB, XBXb, or XbXb
she has XBXB, she is not color blind
 If
she has XBXb, she is not color blind
(the B is dominant to the b so this
woman is a just a carrier of the trait)
 If
she has XbXb, then she is colorblind.
A woman has the genotype XbXb and a man has
the genotype XbY .
 Are either of them colorblind?
Yes both because they each have the recessive alleles (b) for
them.
 If
these two individuals had children what is the
likelihood that their children would be
colorblind?
100%
This
is why there are many
more males that are color blind
than females.
Calico coloration
Male Pattern Baldness