Chapter 23.2, Problem 3R

Summary Introduction

To review:

(a) The positions, which encode amino acids, which may have changed due to positive selection.

(b) The positions, which encode amino acids, which may have changed due to purifying selection.

Given:

The following data was obtained by comparing the gene sequences of many genes encoding surface proteins in influenza viruses (Table 1):

Table 1: Synonymous and nonsynonymous substitutions at particular codon positions.

Codon position	Synonymous substitutions	Nonsynonymous substitutions
12	0	7
15	1	9
61	0	12
80	7	0
137	12	1
156	24	2
165	3	4
226	38	3

Introduction:

A single-base substitution that does not lead to a change in the amino acid encoded by the gene is known as a synonymous substitution. A single-base substitution that changes the amino acid at a particular position is called a nonsynonymous mutation.