Suppose a segment of mitochondrial dna (mtdna) is compared between two similar modern-day species. it is known that this segment of mtdna changes at a steady rate of one base pair every 4 million years. compare the sequences of the two mtdna segments given below. species a: gcactaagcatcgattt species b: gcaccaggcactggttc use the basic principle of molecular clocks to calculate how long ago the two species diverged from a common ancestor.