Question

A phenotypically normal woman is heterozygous for the recessive Mendelian allele causing phenylketonuria, a disease caused by the inability to process phenylalanine in food. She is also heterozygous for a recessive X-linked allele causing red–green colorblindness. What percentage of her eggs will carry the dominant allele that allows normal processing of phenylalanine and the X-linked recessive allele that causes colorblindness?

A) 0%
B) 25%
C) 50%
D) 75%
E) 100%

Answer 1

The correct answer is B. 25% of eggs.

Step-by-step explanation:

A phenotypically normal woman is heterozygous for:

• The recessive Mendelian allele causing phenylketonuria: Pp

• The recessive X-linked allele causing red-green colorblindness: XRXr

This woman´s genotype is Pp XRXr

The woman´s possible gametes are: XR P, XR p, Xr P, Xr p

Each gamete has 25% of the possibilities to occur. The gamete Xr P carries the dominant allele for normal processing of phenylalanine and the X-linked recessive allele for colorblindness. 25% of the eggs will present these alleles.