1. Examine the nucleotide that has been found in the first position of one of th

Question

1. Examine the nucleotide that has been found in the first position of one of the exons of the gene X across several species. Assume that in the ancestor there was also an A in that position. Indicate which evolutionary scenario is the most parsimonious (=plausible): (a) the one involving the mutation from A to G before the split between the lineages that lead to chimps and humans (blue arrow); or (b), that involving the mutation from A to G after the split of the mentioned lineages (double headed green arrow).

Explanation / Answer

The most plausible scenario is that the mutation occurred at the blue arrow mark, when 2 lineages emerged from the putative ancestor bearing A at that location. Those descendants that kept the A would then be the ancestors of today's macaques. The descendants of those who mutated that A to a G came to be ancestors of a common ancestor for chimps and humans. This would be the simplest and most parsimonious scenario.

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