Question 1
Paper 2Hard16 marksA family has several members diagnosed with phenylketonuria (PKU). Figure 1 shows their pedigree. No other family members are shown.
Use P for the allele not associated with PKU and p for the PKU-associated allele.
Using Figure 1, state two observations that support PKU having an autosomal recessive inheritance pattern in this family.
Deduce the genotypes of I-1, I-2, II-2 and II-3.
Show the genetic cross for a child of II-2 and II-3, and state the probability that this child has PKU.
III-2 does not have PKU. Determine the probability that III-2 is a carrier of the p allele. Show your reasoning.
Suppose III-2 has a child with a person known to be a Pp carrier. Determine the probability that their child will have PKU. Use your answer to part (d).
Explain how inheritance of the p allele can result in PKU and affect the conversion of phenylalanine to tyrosine.