Certain Loci That Are in Linkage Disequilibrium with Alleles of Interest

Multiple Choice

Certain loci that are in linkage disequilibrium with alleles of interest can be used as markers,which can then be useful in reconstructing the history of those alleles in populations.One such marker/allele is described in your text,where the allele in question has an insertion mutation,rendering an enzyme (glucocerebrosidase,or GBA) nonfunctional.The decay curve for linkage disequilibrium between this marker (named D1S305) and the nonfunctional GBA allele is shown in the accompanying figure.The orange lines show the present level of linkage disequilibrium and the inferred number of generations elapsed since the most recent common ancestor.Assuming an average generation time of 25 years,what is the best estimate for how long ago the most recent common ancestor existed?

A) about 55 years ago
B) about 1375 years ago
C) about 2325 years ago
D) There is insufficient data to make this determination.