Chapter 5, Problem 15P

A DNA variant has been found linked to a rare autosomal dominant disease in humans and can thus be used as a marker to follow inheritance of the disease allele. In an informative family (in which one parent is heterozygous for both the disease allele and the DNA marker in a known chromosomal arrangement of alleles, and his or her mate does not have the same alleles of the DNA variant), the reliability of such a marker as a predictor of the disease in a fetus is related to the map distance between the DNA marker and the gene causing the disease.

Imagine that a man affected with the disease (genotype Dd) is heterozygous for the V and V forms of the DNA variant, with form V on the same chromosome as the D allele and form V on the same chromosome as d. His wife is V V dd, where V is another allele of the DNA marker. Typing of the fetus by amniocentesis reveals that the fetus has the V and V variants of the DNA marker. How likely is it that the fetus has inherited the disease allele D if the distance measured in a two-point cross between the D locus and the marker locus is (a) 0 m.u., (b) 1 m.u., (c) 5 m.u., (d) 10 m.u., (e) 50 m.u.?