Deafness Is Often Inherited in Humans as an Autosomal Recessive

Multiple Choice

Deafness is often inherited in humans as an autosomal recessive trait. Assume that this is the case here. Two severely deaf people meet and marry. They have four children and all of them have normal hearing. What is the MOST reasonable explanation for this outcome?

A) The mutant allele for deafness shows variable expressivity and the normal children may have some hearing loss that is difficult to detect.
B) Complementation has occurred in the children, indicating that the deafness mutations in the parents involved different genes.
C) Deafness in this family shows a genetic maternal effect with the condition being determined by the genotype of the mother.
D) Deafness in this family is most likely caused by an epigenetic change such as the addition of methyl groups to the DNA.
E) The mutant allele for deafness shows anticipation and becomes more weakly expressed in succeeding generations.