Acertain segment of dna can be used as a molecular clock. its rate of mutation is one mutation per 15 million years. examine the dna segments from two different species: species a: gttgagctagtatggacc species b: gataagctagtaaggtca using this example, explain how this information can be used to determine how long ago these two species shared a common ancestor.

Species A: G T T G A G C T A G T A T G G A C C
Species B: G A T A A G C T A G T A A G G T C A
Differences:    1    1                                   1         1     1

In comparing the species,  I noticed 5 differences. I noted the differences using 1. 

Since the problem states that 1 mutation occurs per 15 million years, it is safe to say that the two species shared a common ancestor 75 million years ago.

5 mutations * 15million yrs/mutation = 75 million years.