Polydactyly is an autosomal dominant disorder. A man who is homozygous for polyd
ID: 312591 • Letter: P
Question
Polydactyly is an autosomal dominant disorder. A man who is homozygous for polydactyly has an extra digit on his left hand. His spouse has a normal genotype and phenotype regarding polydactyly. At the population level, this trait is 50% penetrant among heterozygotes. Which of the following is correct regarding their children? Select ALL that apply.
a)the probability that each of their children will be affected is 1 in 4.
b) If their first child is affected, then if they have another child, it is not expected to be affected.Explanation / Answer
b) If their first child is affected, then if they have another child, it is not expected to be affected ----> TRUE (because 50% of the offspring are likely to be affected)
e) The probability that each of their children will be affected is 1 in 2. ---> TRUE
Assume that the gene coding for polydactyly is A and the gene coding for normal phenotype is, a; A is dominant over a. Given that the father is homozygous dominant (AA) and the mother is homozygous recessive (aa). And the gene penetration is 50% in heterozygotes.
Cross between them will have the progeny with the following genotypes:
AA* aa -à Aa (All heterozygous).
As the penetrance is 50%, the chances of each child to be affected is 50% or 1 in 2.