The following pedigree concerns the autosomal recessive disease phenylketonuria (PKU). The couple marked A and B is contemplating having a baby but is 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.

The following pedigree concerns the autosomal rece