Phenylketonuria (PKU) is a disease that results from a recessive gene. Two normal parents produce a child with PKU.

(a) What is the probability that a sperm from the father will contain the PKU allele?

(b) What is the probability that an egg from the mother will contain the PKU allele?

(c) What is the probability that their next child will have PKU?

(d) What is the probability that their next child will be heterozygous for the PKU gene?