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

Question

Quizplus · Accepted Answer

Germline mosaicism in one of the parents is the most likely explanation for unaffected parents having two children with a highly-penetrant, autosomal dominant disorder. This condition occurs when some of the parent's germ cells (sperm or eggs) carry a genetic mutation, but the mutation is not present in the parent's somatic (body) cells, making the parent unaffected by the disorder but capable of passing the mutation to their offspring.

What Is the Most Likely Explanation for a Set of Unaffected