31. A couple who are planning to have a child visit a genetic counselor for advi

Question

31. A couple who are planning to have a child visit a genetic counselor for advice. At the suggestion of their doctor, the wife (1lI-2) was genotyped for a panel of disease alleles and she came up positive as a carrier of a rare recessive autosomal cardiovascular disease. The husband (Il-1) is healthy and clearly does not have the disease but mentions that his paternal grandfather (-1) died at a young age from a cardiovascular disease and his maternal grandmother (I-4) also suffered from some kind of cardiovascular condition. Assume that the wife is a carrier for the same disease as the husband's paternal grandfather and maternal grandmother. (a) What is the probability that the couple will have a child with the disease? (b) If the cardiovascular condition has a penetrance of 80%, would that affect your answer to problem 4? If so, what is your new answer? 1-1 I-2 I-3 1-4 11-1 1l-2

Explanation / Answer

Inheritance pattern: Autosomal recessive

WT dominant allele = C

Mutant recessive allele = c

II-1 to be carrier = 100% = 1 (One of the parents is homozygous)

= Cc

II-2 to be carrier = 100% = 1 (One of the parent is homozygous)

= Cc

Parental cross: II-1 X II-2 = Cc X Cc

Progeny: CC Cc Cc cc

The probability for III-1 to be a carrier (Cc) = 50% = 0.5

The probability for the kid to be affected = 0.5 X 0.25 = 0.125

If the phenotype shows 100% penetrance, there is a 12.5% probability that child can be affected by the disease.

If the phenotype shows 80% penetrance, there is a 12.5 X 0.8 = 10% probability that child can be affected by the disease.

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