Question

Suppose species 1, 2, and 3 are endemic to a group of islands (such as the Galápagos) and are all descended from species 4 on the mainland (which will serve as an outgroup; its very large population size means that no new mutations have become fixed in its population in the time since the islands were colonized). We sequence a gene and find ten nucleotide sites that differ among the four species (among many other loci that do not vary). The nucleotide bases at these sites are:

Species 1: GCTGATGAGT

Species 2: ATCAATGAGT

Species 3: GTTGCAACGT

Species 4: GTCAATGACA

Estimate the phylogeny of these taxa by plotting the changes on each of the three possible trees and determine which tree requires the fewest evolutionary changes.

Answer 1

Answer :)

If all species are descended from species 4, we need to score the gene sequence:

By comparing Species 3 and Species 4:

Species 3: GTTGCAACGT

Species 4: GTCAATGACA

Score = – 8

The nucleotides in bold letters do not match the sequence of species 4.

By comparing Species 2 and Species 4:

Species 2: ATCAATGAGT

Species 4: GTCAATGACA

Score = – 3

By comparing Species 1 and Species 4:

Species 1: GCTGATGAGT

Species 4: GTCAATGACA

Score = – 4

Therefore, Species 3 is the most deviated species from species 4, and the other two species i.e. 1 and 2 are closer in the phylogenetic tree.

The following image is showing the phylogenetic tree: