Male-limited precocious puberty results from a rare autosomal allele (P) that is dominant over the allele for normal puberty (p) and is expressed only in males. A male and female that both went through normal puberty have two sons. The first son undergoes precocious puberty but the second undergoes normal puberty.
-What is the genotype of the mother?
A) PP
B) Pp
C) pp
D) PP or Pp
E) Pp or pp

Question

Male-limited precocious puberty results from a rare autosomal allele (P) that is dominant over the allele for normal puberty (p) and is expressed only in males. A male and female that both went through normal puberty have two sons. The first son undergoes precocious puberty but the second undergoes normal puberty. 
-What is the genotype of the mother?
A) PP
B) Pp
C) pp
D) PP or Pp
E) Pp or pp

Quizplus · Accepted Answer

The mother must be heterozygous (Pp) because she has two sons, one with precocious puberty (PP) and one with normal puberty (pp). If the mother were homozygous dominant (PP), both sons would have precocious puberty. If the mother were homozygous recessive (pp), neither son would have precocious puberty.

Male-Limited Precocious Puberty Results from a Rare Autosomal Allele (P)