Question

Mike and Wendy (IV-3 and IV-4) wish to wed but become aware that they share a common great-grandmother (I-2). In researching their common ancestors mentally retarded due to phenylketouria (PKU). The incidence of PKU carriers in the population is 1 in 50. The probability that their first child will be affected by PKU is: 43 they find that Wendy's grandmother (I-3) had a sister who was A) 1/192 B) 1/256 C) 1/512 D) 1//768 E) none of the above 2

Answer 1

In these cases pKU is autosomal recessive disease

Both parents are normal genotype may AAlAa

Then in case both parents AA. x .AA 0% CHANCE BEING DISEASE

But if both parents are heterozygous for trait disease probability should be 1/4

So answer is none