You know from the fossil record that Sp. 1 and Sp. 2 last shared a common ancest

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Question

You know from the fossil record that Sp. 1 and Sp. 2 last shared a common ancestor 10 million years ago. Assuming a molecular clock what is your best estimate for the age

of the genome duplication event that gave rise to the two paralogs?

Q1) You sequence the genes scn4aa and scn4ab in two fish species (Species 1 and 2). The table below gives your estimates of the number of substitutions that have occurred between the different paralogous and orthologous copies of the gene. Sp. 1 Scn4aaSp. 1 Scn4ab Sp. 2 Scn4aaSp. 2 Scn4ab 10 250 250 10 250 Sp.1Scn4aa 250 Sp. 1 Scn4ab Sp. 2 Scn4aa Sp. 2 Scn4alb

Explanation / Answer

During evolutionary studies, two lineages of fishes, the mormyrids from Africa and the gymnotiformes of South America were observed. These two lineages of fishes were unrelated. But, during course of evolution, they had evolved similar myogenic signalling structures, that generated electrical signals. The signalling organs were found to be related to the voltage gated sodium channels in skeletal muscles, which in turn were specific to teleost fishes.

Sodium channel genes are designated as scn4a genes. Modification in these genes, compromise the function of the sodium channels. Thus, these genes were evaluated to detect their alteration over a time during evolution, and still retain their functional entity.

It was detected that, during evolution, the scn4a genes underwent duplication into two sets, designated as scn4aa and scn4ab, and thus, paralogous, and orthologous copies of the genes are created. Though a set of sister genes as scn4aa and scn4ab, remained functional as skeletal muscle, sodium channel, the other set of as scn4aa evolved to have a new function of signal transduction.

In the given study; the scn4aa and scn4ab genes in species 1 and species 2 fishes, have undergone substitution during a certain period, in course of evolution.

Considering the molecular clock hypothesis:

Given age of shared ancestor = 10 million years (Ti).

Age of genome duplication (T)= 10000000 x 2/500= 40,000 years approximately.

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You know from the fossil record that Sp. 1 and Sp. 2 last shared a common ancest

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