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+.