Question

Using molecular clock, it was estimated that two species A and B must have diverged from their common ancestor about 9x10^6 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 pair that differ between the two species now? Please explain how to solve this.
(A) 0.0270 (B) 0.0135 (C) 0.00017 (d) 0.0035

Answer 1

Right.

The simplest way to use a molecular clock is to compute or estimate the time since two species diverged. A molecular clock is a sequence of DNA - usually from a coding region which makes an essential protein, like the often used ribosomal subunit proteins - with a constant and usually low mutation rate.

0.0015 mutations per million years is quite low.

A molecular clock works by comparing the differences in that gene in two different species. If the sequences are similar, the species diverged recently. If the sequences are quite different, they diverged a long time ago.

It is important to note that molecular clocks are an estimate. That is not noted as often as it should be. Sometimes the same mutation occurs in both the target and the reference sequence. Sometimes a back mutation occurs in an already mutated base so it is back to its initial sequence. These all tend to underestimate the time since the species diverged. What you calculate is a bound on an estimate, not an absolute and correct value. Just keep that in mind...

Answer 2

The problem gives you that the species diverged 0.9 million years ago. It gives you a mutation rate of 1 mutation per 0.0015 million years. To get the number of mutations which have occurred, you multiply and cancel the units.

Answer 3

@blues thank you friend....one more question coming up