A gene family has been accumulating nucleotide substitutions at a rate of 0.25 per million years.On average, there have been 80 substitutions between the common ancestor of this gene family and each of the various living forms of this gene.Based on these numbers, this gene family likely originated _______ million years ago.

Question

Quizplus · Accepted Answer

To determine the origin of the gene family, we need to use the number of substitutions accumulated between the common ancestor and the present forms of the gene. The rate of nucleotide substitutions is given as 0.25 per million years. Therefore, the total number of substitutions that occurred in x million years is 0.25x.

The number of substitutions between the common ancestor and each of the various living forms is given as 80. Therefore, the total time elapsed since the origin of the gene family is:

total number of substitutions / substitutions per million years
= 80 / 0.25
= 320 million years.

Hence, the gene family likely originated about 320 million years ago, which corresponds to answer choice E.

A Gene Family Has Been Accumulating Nucleotide Substitutions at a Rate