Because of redundancy in the genetic code, some changes to sequence do not lead
ID: 273750 • Letter: B
Question
Because of redundancy in the genetic code, some changes to sequence do not lead to changes in amino acids. Such changes are called "synonymous" changes, and others that do change the amino acid are called "non-synonymous." if one aligns two genes between species, one can look to see whether differences are synonymous or nonsynonymous. Let’s assume that synonymous changes are completely neutral, while nonsynonymous changes are not.
(a) Suppose at all synonymous sites, the observed pattern of differences leads to an estimated rate of substitution of 1 x 10-8 per site per generation. What would you estimate the total mutation rate per site to be?
(b) Suppose that at non-synonymous sites the estimate of the rate of substitution is 2.5 x 10-9 per site per generation. Using your answer from (a), what is your estimate of the fraction of neutral mutations at non-synonymous sites?
(c) Suppose instead that at non-synonymous sites the estimate of the rate of substitution is 2 x 10-8 per site per generation. What might explain the non-synonymous to synonymous rate ratio observed?
Explanation / Answer
a. mutation rate will be the same as substitution rate as synonymous sites will cause mutation of 1 * 10-8 per generation.If we consider duplication of these two genes then the total mutation rate will be 0.25 *10-8 per site after replication.