The Following Pedigree Concerns the Autosomal Recessive Disease Phenylketonuria (PKU)

Multiple Choice

The following pedigree concerns the autosomal recessive disease phenylketonuria (PKU) .The couple marked A and B are contemplating having a baby but are concerned about the baby having PKU.What is the probability of the first child having PKU? Unless you have evidence to the contrary,assume that a person marrying into the pedigree (i.e.,not a descendant of the two parents at the top of the pedigree) is not a carrier.The filled-in individuals have PKU.

A) 0
B) 1/12
C) 1/4
D) 3/4
E) 9/64