Question

A woman, Melanie, and a man, Allan, who are both carriers for phenylketonuria (a rare autosomal recessive disease) have two daughters, Jessica and Andrea, and two sons, Kyle and James. None of Melanie and Allan's parents, or their siblings, had phenylketonuria. However, both of their sons have the disease.

1) What percentage of Melanie's eggs will carry the phenylketonuria allele?

2) What percentage of Allan’s sperm will carry the phenylketonuria allele?

3) Among Melanie and Allan's four children, how does the observed frequency of affected children compare to the expected frequency? Does the observed result go against the concepts of Mendelian genetics? Explain

Answer 1

1. 50%.

Since Melanie's is a carrier for phenylketonuria which is an autosomal recessive disease ,it means Melania is heterozygous for this trait and therefore 5o% of her eggs will carry ohenylketonuria allele.

2. 50%.

Since Allan is carrier for phenylketonuria which means he is heterozygous for this trait and therefore half of his sperms ie 50% seems will carry ohenylketonuria allele.

3. Expected frequency would have been

Pp x Pp

Offsprings : PP (normal) Pp (carrier) Pp (carrier) pp (affected)

1/4 children will be affected .

But observed frequency is 2/4 is affected.

No ,observed frequency does not go against the Mendelian genetics it only shows that there was frequency of 25% of affected child and two out of 4 children are affected.