Certain Loci That Are in Linkage Disequilibrium with Alleles of Interest

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,how many years total will be required for the linkage disequilibrium reach 0.2?

A) about 55 years total
B) about 100 years total
C) about 1000 years total
D) about 2500 years total
E) There is insufficient data to make this determination.