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.