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%

Question

Quizplus · Accepted Answer

Since the woman is heterozygous for the phenylketonuria allele, 50% of her eggs will carry the dominant allele for normal phenylalanine processing. Being heterozygous for an X-linked recessive trait means that 50% of her X chromosomes carry the allele for colorblindness. The probability that an egg will carry both the dominant allele for phenylalanine processing and the X-linked recessive allele for colorblindness is the product of the two independent probabilities: 50% * 50% = 25%.

A Phenotypically Normal Woman Is Heterozygous for the Recessive Mendelian