In four taxa (A, B, C and D), two characters (shape and color) were scored to infer their phylogenetic relationship. The two character states for shape were square and round, while the two character states for color were black and yellow. The character distribution is given in the table below.

Using the above data, four trees were built using the method of maximum parsimony which are given below.

​Select the option that represents the two most parsimonious trees​

Correct option is D

Parsimony principle: The most parsimonious tree is the one that requires the fewest number of character state changes (minimum evolutionary steps).

Tree A:

• Shape: One change from square to round.
• Colour: One change from black to yellow.
• Total steps = 2 (One for shape, one for color)

Tree D:

• Shape: One change from square to round.
• Colour: One change from black to yellow.
• Total steps = 2 (Again, one for each character)

Hence, both A and D require only two steps each, making them the most parsimonious trees.

Tree B and C:

• Tree B and C each require more than two steps, especially with additional reversals or convergent changes, making them less parsimonious.

Information Booster:

1. Maximum Parsimony in phylogenetics chooses the tree that minimizes character changes.
2. It is based on Occam’s Razor, favoring the simplest explanation with the least assumptions.
3. In the given dataset, only two character state changes (one each in shape and color) are sufficient in trees A and D.
4. Shape transition likely occurred once, from square (ancestral) to round (derived) in a single lineage.
5. Color transition also occurred once, from black (ancestral) to yellow (derived).
6. Trees B and C imply multiple independent transitions, which is less likely evolutionarily.
7. Maximum parsimony is best used with discrete morphological or molecular traits where evolutionary rates are assumed to be low.

Additional Information (Incorrect Options):

• Option 1 (A and B):Tree B requires more character changes, likely two for shape and one for color (total 3), so less parsimonious.
• Option 2 (C and D):Tree C requires additional steps in either shape or color transitions, making it less parsimonious.
• ​Option 3 (B and C): Both trees are suboptimal in terms of minimizing changes.​