Chapter 23, Problem 3Q

Summary Introduction

To analyze:

The expected number of synonymous substitution on the basis of the rate of synonymous substitute provided in the previous question, the time of divergence and number of generations, which take place every year, and the reason for the discrepancy between observed value and expected value.

Given:

The separation of Drosophilia melanogaster from the Musca domestica (houseflies) occurred about 90 MYA (million years ago). It is assumed that there are 174 synonymous substitutions between these two taxa. It is also assumed that the number of generations remains five per year across these two species.

Introduction:

By studying the molecular evolution pattern of the genes, biologists are able to make about the inferences about the types of natural selections that have been operating in nature. Such inferences are important to study the functions of the gene and their evolution over the time, in response to the new environmental conditions.

On the basis of the given data, it is observed that one exon of a random gene is sequenced in four species. The data of synonymous and nonsynonymous substitutions and the phylogeny of the species of the Drosophila species are given. There are 2,000 nonsynonymous and 600 synonymous substitutions sites of the exon.