A Phenotypically Normal Man Has Phenotypically Normal Parents but He

question 20

Multiple Choice

A phenotypically normal man has phenotypically normal parents but he has a sister who has cystic fibrosis caused by a recessive mutant allele. What is the probability that the man is heterozygous for the cystic fibrosis allele?

• A) 1/4
• B) 1/2
• C) 3/4
• D) 2/3
• E) 1/3