Question

Imagine that you have the DNA sequences from the intron of a gene in three species called A, B, and C. Species A and B are most closely related, while C is more distantly related. The sequences of A and B differ by 18 base pairs, A and C differ by 26 base pairs, and B and C differ by 28 base pairs. Fossils show that species A and B diverged about 1.2 Mya, but there is no fossil evidence as to when the most recent common ancestor of all three species lived. Use the genetic data to estimate that date. What assumptions are you making to get this estimate?

Answer 1

Genetic distance is a measure of the genetic divergence between species or between populations within a species, whether the distance measures time from common ancestor or degree of differentiation.

According to the data given in question it is clear that A and B are closer enough. There may be possibility of linkage.

Two genes that occur on the same chromosome are said to be linked, and those that occur very close together are tightly linked. Study of linkage provides information about the relative position of genes on chromosomes, allowing the construction of chromosome maps.

There are chances that A and B can inbreed with each other. In later generation developed, distance between genes will go on increasing as compared to C. C was already at higher distance from both A and B. So C will get evolved into a new branch of phylogenetic tree. A and B will move together for sometime due to their closeness and will get placed themselves on different branches of phylogenetic tree after a significant time period.