Question

A group of scientists determines that a mitochondrial DNA sequence shared by two species has a constant mutation rate. The sequences of mitochondrial DNA for the two species are shown below.

Species A: GACTGGGCATTA
Species B: GACCGGACATGA
Using the principles of molecular clocks and a known mutation rate for this sequence, the scientists determine that these species diverged from a common ancestor 30 million years ago. Based on this information, how much longer do you predict it would take these species to differ by a total of seven base pairs?
60 million years
20 million years
140 million years
40 million years

Answer 1

The answer is 60 million years.

Answer 2

The correct answer would be 40 million years.

The molecular clock is a technique used to determine the time when the two species diverged from a common ancestor. It uses the mutation rate to determine the same.

Mutation rate is the rate at which a number of mutations take place in a given unit time.

If we compare the DNA sequence of the given two species, we would find that three mutations have taken place in thirty million years.

Species A: GACTGGGCATTA

Species B: GACCGGACATGA

Thus, the mutation rate of the species is one mutation per 10 million years.

The DNA sequences already have 3 mutations. Thus, for a total of 7 mutations, 4 mutations are required.

Thus, in 40 million years the two DNA sequences would differ by 7 nucleotides.