A Man Is Heterozygous for a Rare Trait That Is

question 92

Multiple Choice

A man is heterozygous for a rare trait that is assumed to be caused by a dominant autosomal mutant allele. He marries a woman who is phenotypically normal. They have a phenotypically normal daughter who marries a phenotypically normal man. Unexpectedly their first child, a girl, has the same abnormal trait as her grandfather. Which of the following BEST explains this situation?

• A) The trait is really due a mutation in a cytoplasmic gene and can be only inherited from the mother.
• B) This is a sex-influenced trait and is expressed more often in females than in males.
• C) This is an example of genomic imprinting and the mutant allele is only expressed if it is inherited from the father.
• D) The mutant allele shows incomplete dominance when heterozygous with the normal allele.
• E) The mutant allele shows reduced penetrance and the normal daughter carries the mutant allele.

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