A restriction-fragment length polymorphism at a site in the X chromosome has three alleles, A₁, A₂, and A₃. The gel below is the DNA fingerprint for two girls who have the same parents. What is the genotype of the mother? Of the father?

Question

Quizplus · Accepted Answer

The bands in the gel correspond to the alleles A₁, A₂, and A₃. Each individual has two alleles at this locus. The two girls have identical band patterns, suggesting that they are homozygous at this locus. The only way for them to be homozygous for the same allele is if each parent contributed one of the same alleles to each daughter. This means that the genotypes for the parents are A₁/A₃ for the mother and A₂/A₃ for the father.

A Restriction-Fragment Length Polymorphism at a Site in the X