A woman, Melanie, and a man, Allan, who are both carriers for phenylketonuria (a

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.
Answer questions 1 to 8 based on this scenario. Please use P to indicate the dominant allele for this condition and p to represent the recessive allele.

1) What are Melanie and Allan's genotypes?

2) Based on the scenario given, what are the most likely genotypes of Melanie's parents and of Allan's parents?

3) What are the genotypes of each of their daughters? What are the genotypes of their sons?

4) What percentage of Melanie's eggs will carry the phenylketonuria allele? What percentage of Allan’s sperm will carry the phenylketonuria allele?

5) Melanie is pregnant and she and Allan have just found out the sex of the fetus is male. What is the probability the fetus is carrying two copies of the recessive phenylketonuria allele, and thus will be affected with the disease?

6) 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?

Explanation / Answer

1) Genotype of Melanie is Pp

Genotype of Allan is Pp

2)The most probable genotype of melanie and allan parents can be

Pp x Pp, PP x pp, PP x Pp, pp x Pp

3) Since daughters are normal so their genotype will be PP

Diseased son will have pp

5) chances of the featal male to have phenylketonuria will be 25% since their offspring will have 3 possible genotypes PP 25%, Pp 50% and pp 25%. Diseased child will have a genotype pp.

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