Question

Why do we expect to see more synonymous substitutions than non-synonymous substitutions if a locus is under purifying selection? In your answer, be sure to explain what synonymous vs. non- synonymous substitutions and purifying selection are. : BIU A - A - Ix E 3 MB NVX 6 0 3 3 x © All x 12pt HTML Editora = - Paragraph - O words Question 27 2 pts In some birds such as phalaropes, males provide all of the parental care to offspring, and females compete with one another for access to males and breeding territory. In this species, would you expect males or females to be larger and more brightly colored (or would they be the same)? Explain your answer.

Answer 1

Synonymous substitution :

It is the evolutionary substittution of a one base with another in the exon region of a gene coding for a protein such that the the resultant amino acid sequence is unchanged.

Non-synonymous subsitution :

It is the evolutionary substitution of one base with another in the exon region of a gene coding for a protein such that the resultant amino acid sequence is changed.

Purifying selection :

Purifying selection can be defined as a selection which reduces the frequency of a deleterious mutation or completely eliminates it.

When a locus is under purifying selection, we expect to see more synonymous selections than non-synonymous selection. In general, non-synonymous commonly cause deleterious mutations which are hazardous for the cell. So under purifying selection, most non-synonymous substitutions are selected against. However in the mean time synonymous substitutions can accumulate since they do not affect the protein's amino acid sequence. Thus we observe a higher number of synonymous substitutions.

Q.27.

In case of birds like Phalaropes, males provide the parental care and incubate the eggs. On the other hand, females fight for access to males and territory. After mating, females desert the males leaving the eggs with the males for caring. It is a typical case of sex role reversal. So in this case we expect the females to be larger since they have to compete and fight over to get the best caring male partner and also territory. They are expected to be brighter since colourful plumage is a visual indicator of the reproductive health and overall health of that particular female. In addition, colourful plumage also serves as a essential tool in courtship rituals to attract the sexual partner.