Question

You are examining the following human pedigree and want to determine if the rare dominant disease allele (D) is linked to a specific DNA sequence location, referred to as a "molecular marker." You are using two molecular markers, R1 and R2. Parental and progeny genotypes and phenotypes are indicated. Note that the father is a dihybrid at both loci, but the mother is homozygous recessive at both loci and linked to R1 (d-R1/d-R1). There is complete penetrance of the trait and a linkage phase of D-R1/d-R2 in the father. Assuming that the marker and the gene are linked, what is the best estimate of the map distance between the two loci?

a) 15 CM
b) 20 CM
c) 25 CM
d) 30 CM

Answer 1

The best estimate of the map distance between the two loci is 25 CM.

Step-by-step explanation:

When genes are located on the same chromosome, they are considered linked. In this case, the rare dominant disease allele (D) is linked to a specific DNA sequence location referred to as a 'molecular marker,' which in this case is R1.

The father is a dihybrid and homozygous recessive at the other locus, and the mother is homozygous recessive at both loci and linked to R1. The phenotype for the disease allele and R2 is completely penetrant. Based on the given information, the best estimate of the map distance between the two loci is 25 CM (c).