Which person is an obligate carrier of an autosomal-recessive single-gene trait or disorder without expressing the trait or disorder?
A)The son of a man with classic hemophilia
B)The daughter of a woman with Marfan syndrome
C)The son of a man who expresses a widow's peak hairline
D)The daughter of a woman who expresses attached earlobes

Question

Quizplus · Accepted Answer

Attached earlobes (versus free-swinging earlobes) is an autosomal-recessive trait. A person who expresses this trait is homozygous for the allele and transmits the allele to all his or her children regardless of the type of earlobes any of them express. This makes them obligate carriers of the allele for earlobe attachment. The hemophilia gene mutation is on the X chromosome, which a father cannot transmit to his son. Marfan syndrome and widow's peak are autosomal-dominant traits for which there is no carrier status. If the allele is present, it is expressed.

Which Person Is an Obligate Carrier of an Autosomal-Recessive Single-Gene