Adaptation model: •Duplication creates redundancy •One copy gains new beneficial

Question

Adaptation model:

•Duplication creates redundancy

•One copy gains new beneficial function through mutation(s), then loses ancestral function

•Other copy preserves ancestral function

What pattern do we expect for DN/DS?

Both copies should show DN/DS >> 1.

The copy that acquired the new function should have DN/DS >> 1, and the copy that maintained ancestral function should have DN/DS ~1.

The copy that acquired the new function should have DN/DS << 1, and the copy that maintained ancestral function should have DN/DS >> 1.

The copy that acquired the new function should have DN/DS >> 1, and the copy that maintained ancestral function should have DN/DS << 1.

Explanation / Answer

The answer will be the copy that acquired the new function should have DN/DS >> 1 & the copy that maintained ancestral function should have DN/DS ~1 (Option b).

Explanation: Evolution is driven by both natural (has effect on phenotypes) & neutral selection (has little effect on phenotypes). In natural selection beneficial changes occur. It is of two types- positive selection (Also called Darwinian selection) promotes beneficial alleles & negative selection (Also called purifying selection) removes deleterious alleles. To know if the changes in amino acid sequence is due to natural selection or neutral selection one can use the dN/dS ratio. It compares the rate of nucleotide substitutions at synonymous sites (dS), i.e., neutral & the rate of nucleotide substitutions at non-synonymous sites (dN), i.e., natural selection. If this ratio is closed to 1 then we assume that neutral selection takes place, if it is greater than 1 then positive selection takes place & if it is less than 1 then negative selection takes place.

In the question gaining of beneficial function occurs, i.e., positive selection. So, in that case dN/dS ratio will be greater than 1. Also the copies which preserves the ancestral function, show neutral selection. In that case dN/dS ratio will be closed to 1. So, the correct answer will be option b.

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