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Sex Linked Genes
Location
Sex linked genes are typically located on
the X chromosome.
 No corresponding gene on the Y
chromosome.

Sex-Linked Traits
Hemophilia
 Color deficiencies
 Calico cats!

Queen Victoria
was a carrier for
hemophilia
Who it affects most



Sex linked recessive
traits are more likely
to affect men than
women.
Why do you think that
happens?
Men have only one
X chromosome.
The Transmission of Sex-Linked Recessive Traits
Mother homozygous dominant (XAXA), father has
recessive trait (XaY).
a.

Daughters are carriers, sons normal.
Female carrier mates with normal male.
b.

½ sons have trait, ½ daughters will be carriers.
Female carrier mates with male with recessive trait.
c.


½ daughters are carriers, ½ have trait.
½ sons have trait, ½ do not.
Red-Green Color Deficit
Color deficiencies

“Red-Green” deficiency





Protanopia, Deuteranopia
1% of males, 0.02 % of
females
Missing Long wave length
cones OR
Missing medium wave length
cones
“Blue-Yellow” deficiency



Tritanopia
0.002 % of males, 0.001%
of females
Missing short wave length
cones.
X-linked Trait: Calico Cat

A gene for fur color resides on the X
chromosome.
Kiley!
After getting spayed
X-linked Trait: Calico Cat

A yellow cat has a litter of four kittens: 1
yellow and 3 calico. Assuming that there
is a single father for the litter, what is the
sex of the yellow kitten?
Male
orange Black
Black orange
orange
Black
Black
Black
orange
orange