Question

The following are data from a small portion of the genome from four tetrapods.

Species: Sequence:

Chelonia mydas GACAG

Grus americana GACCG

Taricha granulosa GTACA

Zaglossus attenboroughi GTCAA

The challenge is to reconstruct the evolutionary ancestry of these four species from the molecular sequence information.

1.Phylogeny 1:

a. Draw a potential (unrooted) phylogenetic tree illustrating the possible relationships among these species.

b. Determine what (minimal) changes in sequence are required and where they must be located on the tree you have drawn in order to explain the observed sequences. Mark these on the tree above. HINT: it may be helpful to start with the sequences themselves at the tips of the tree.

c. How many (minimal) changes are required for this tree?

2. Phylogeny 2:

a. Draw a different potential (unrooted) phylogenetic tree illustrating the possible relationships among these species.

b.Mark the (minimal) changes on the tree above.

c. How many (minimal) changes are required for this tree?

Answer 1

We have to stablish 2 different hypothesis of phylogenetic relationship, let's analyze the data and search for the most 2 convincing ones:

1.-

a) Let's analyze the data:

Chelonia mydas GACAG

Grus americana GACCG

Taricha granulosa GTACA

Zaglossus attenboroughi GTCAA

Let us propose a tree that would follow logic based on what we know about animals, and let's see how that ends:

b) Now let's analize the changes needed from one species to all the others. Let's start with Taricha.

- From Taricha to Chelonia we need 4 changes, T to A, A to C, C to A and A to G. That is 4 steps until now

- From Chelonia to Grus we need only 1 change, A to C. That is 5 steps until now

- From Grus to Zaglossus we need 3 more steps, A to T, C to A and G to A. That is 8 steps.

The dark colums are the marked changes.

c) It is 8 changes

2.-

a) Let's try with another configuration, let's say this one:

b) Let's analyze the needed changes:

- From Taricha to Zaglossus we only need 2 changes. 2 steps until now

- From Zaglossus to Chelonia we need only 2 changes. 4 steps until now

- From Chelonia to Grus we need only 1 change. 5 steps finally

The dark colums are the marked changes.

c) It is only 5 changes, this is a more parsimonious tree than the previous one.