28. Using molecular clock, it was estimated that two species A and B must have diverged from their common
ancestor about 9 x 10^6 years ago. If the rate of divergence per base pair is estimated to be 0.0015 per million
years, what is the proportion of base pairs that differ between the two species now?
Answers
If you assume a mutation rate of 5e-10 mutations per base pair per year, and a human-chimp distance of 1.2% or 0.012, the divergence time is about 0.5 * 0.012 / 5e-10 = 12My. That is the puzzle, and it remains whatever convention you use (haploid vs diploid) for stating a number of mutations per generation.
The first term in your equation (0.5 * 5e-10) is half the percentage of the HAPLOID reference genomes that differ between humans and chimps.
The second term in your equation is the mutation rate expressed as the number of mutations per DIPLOID genome per year. We know that the mutation rate is about 100 mutations per generation in a DIPLOID genome. The mutation rate in your equation is based on the number of mutations per year per 6.4e9 base pairs.
5e-10 X 6.4e9 X 30 years = 96 mutations/year