Bio question from ADA 2009 test

[Dental2000]

Suppose an animal has a gene for coat color that is sex-linked (X-linkage) and incompletely dominant, and in which females with an AA genotype have a black coat color; aa individuals have a yellow color; and those with Aa have a marble coloration. If a marble female was crossed with a yellow male, then each of the following might result under normal Mendelian conditions EXCEPT one. Which one is the EXCEPTION?

1)Black male
2)Black female
3)Yellow male
4)Yellow female
5)Marble female

---

Members don't see this ad.

 

[Demps]

Answer is B. Black Female. You will not get a black female from this cross.

You're given marble-colored female - possessing X^A and X^a

This female is crossed with yellow-colored male - possessing X^a and Y

Everytime you do sex-linked cross. Male is hemizygous and only has one X chromosome as you see.

if you do the punnett square, you will see that the resulting phenotypes are following

25% marble female (Aa)
25% yellow female (aa)
25% black male (A)
25% yellow male (a)

Hence, you won't see any black female. Answer is choice B