Suppose that you compare the levels of nonsynonymous and synonymous substitution

Question

Suppose that you compare the levels of nonsynonymous and synonymous substitutions (i.e. you perform the kA/kS test) on a particular coding region of a gene. You find that kA/kS = 0.3.

(a) What type of selection, if any, would this result support?

(b) You also examine levels of polymorphism around this particular gene in a sample of 20 individuals from the population of interest. You find that Tajima’s D is -3.1. What type of selection, if any, would this result support?

(c) Provide 2 explanations for why the kA/kS test and the Tajima’s D test appear to give contradictory results.

Explanation / Answer

ans- A this is a positive selection because the ratio of kA/kS are less than 1.

ans-b here in this case the type of selection is balancing because here the value of D is less than zero which indicate that the number of rare alleles present is low.

ans-c first the kA/kS Test indicate that the synonyms mutation are high in number which means that rare allele should be present while the D value indicate that the rare alleles are very less.

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