Answer If two hereizygous carrier of phenylketonuria marry and plant to give birth to five children, then 25% of child will be normal, 25% affected and 50% carrier.it can also be shown from given below presentation: Heterozygous carrier x Heterozygous carrier K/k+. X. K/k+ Gametes. K,k+,k,k+ F1 offspring KK, kk+, kk+,k+k+.