Problem

Solutions For An Introduction to Genetic Analysis Chapter 2 Problem 67P

Step-by-Step Solution

Solution 1

Given below is the pedigree for the family described:

a. In this pedigree, the mode of inheritance is not autosomal dominant because if it is autosomal dominant, then the individual III-3 must inherit the condition.

Therefore, the mode of inheritance must be either autosomal or X-liked recessive disorder. It is recessive because the unaffected parents have affected progeny. Since only males inherited the disease, it is more likely to be X-linked inheritance.

Step #2 of 3

b. Allele 'a' is recessive responsible for the disorder.

Generation I X^A/Y, X^A/X^a

Generation II-> X^A/X^A, X^a/Y, X^A/Y, X^A/X^-, X^A/X^a, X^A/Y

Generation IIIX^A/X^-, X^A/Y, X^A/X^a, X^A/X^a, X^A/Y, X^A/X^A, X^a/Y, X^A/Y, X^A/X^-

Step #3 of 3

c. The first assumption should be that no one marries in that family would carry the recessive allele.

The first couple does not have chance of having an affected child because the son has received the Y chromosome from the father.

The second couple has ¼ or 0.25 probability of having an affected child, as the woman (III-4) is the carrier of the recessive allele, which she has received from the father. No daughter will have the disorder, as they will receive one X chromosome from the father, who is unaffected.

The third couple has no chance of having a child with this disorder. But all their daughters will be carriers of recessive allele.

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