Chapter 3, Problem 45P

A couple wants to know the probability that their expected child will suffer from split-hand deformity, which affects the prospective father, who is indicated by an arrow in the pedigree shown. (The arrow means that he is the proband—the person in the family who first brought the disorder to the attention of medical professionals.) This trait, shown in the following photo, is rare in the population, and the prospective parents are not related to each other.

 

a.	What is the mode of inheritance of this trait?
b.	What is the penetrance of this trait [that is, the ratio between the number of individuals in the pedigree who display the trait (numerator), and the number of individuals you know from the pedigree must have the trait-determining genotype regardless of whether they have the trait or not (denominator)]?
c.	Using your answer to part (b) above, what would you tell the parents about the numerical likelihood their expected child will have split-hand deformity?
d.	Why is it possible that the likelihood the child will be affected is actually less than the number you just answered in part (c)? You should specify the lowest numerical likelihood that could possibly be consistent with the data.