A pedigree shows that two parents are phenotypically normal, but one of their four biological children has a typical autosomal recessive trait.The other three children are phenotypically normal.It is very likely that:
A)the affected child is a girl.
B)the affected child is a boy.
C)the trait was expressed by one of the grandparents of the children.
D)the parents are both heterozygous for the trait.
E)if the affected child eventually marries a phenotypically normal spouse, all of the their children will have the trait.

Question

Quizplus · Accepted Answer

Since the trait is autosomal recessive, it means that both parents must be carriers (heterozygous) for the trait. The affected child then inherits two recessive alleles (one from each parent), while the other three children inherit at least one dominant allele from each parent, making them phenotypically normal. The gender of the affected child is not specified in the question, so we cannot determine whether the affected child is a boy or a girl. The fact that two parents are phenotypically normal also eliminates option C. Finally, since the mode of inheritance is autosomal recessive, it means that the trait is not sex-linked or controlled by mitochondrial DNA, making option E also incorrect.

A Pedigree Shows That Two Parents Are Phenotypically Normal, but One