Question

What is the most likely explanation for a set of unaffected parents having two children with a highly-penetrant, autosomal dominant disorder?

A Two new mutations occurred in the same gene
B Germline mosaicism in one of the parents
C Variable expressivity
D Somatic reversion in carrier parent
E Inactivation of mutant allele in carrier parent

Answer 1

Germline mosaicism in one of the parents is the most likely reason for unaffected parents having two children with an autosomal dominant disorder, allowing them to pass on the mutation without showing any symptoms themselves.

Step-by-step explanation:

The most likely explanation for a set of unaffected parents having two children with a highly-penetrant, autosomal dominant disorder is germline mosaicism in one of the parents (option B). This occurs when some of the parent's reproductive cells (germ cells) carry a genetic mutation, even though the parent's somatic (body) cells do not have the mutation, and thus the parent does not exhibit symptoms of the disorder. This can result in a situation where the parent can have multiple offspring with the disorder even if the parents do not show any signs of the condition themselves.