A white-eyed male is mated to a wild-type female and they have an offspring that is a white-eyed male. What proportion of their offspring will be wild-type males?

Question

a) 0

b) 1/4

c) 1/2

d) 3/4

e) 1

Answer 1

Eye color in fruit flies is a sex-linked (X-linked) gene. Wild type shows the dominant phenotype. Let's pick a letter: E for eyes. In this case, white eyes are recessive so we will give them the allele "e", and wild type are dominant (by definition) so we will give them the allele "E". Since they are linked to the X chromosome, we write them XE and Xe. The other possible chromosome is a Y. Females are XX and males are XY

The parents are therefore:

male: XeY

female: XEX_

We don't know if mom is homozygous XEXE or heterozygous XEXe... but wait! We do!

Since they have a male offspring who has white eyes XeY, then she must have had an Xe to give to him, since he had to get the Y from his dad. Therefore, the female's genotype is XEXe.

If you draw a punnett square, you see their possible offspring are:

XEXe

XeXe

XEY

XeY

The wild type males will be XEY, which appears in 1 out of the 4 possibilities, so the probability is 1.4 (answer b).

Hope that helps!

Answer 2

Hello,

This question has to do with punnett squares and inheritance patterns. More information is needed as far as whether white eyes are dominant or recessive. I would assume recessive, but cannot be sure. The question should tell you this information, it is needed to answer the question. Also, wild type means heterozygous.

I can help you with this concept very easily. Reach out if you would like to schedule something.

-Shaun