Question

A phylogenetic tree for the evolution of two pigmentation traits in species of fish is shown for clades X, Y, and Z. Genes A and/or B, if mutated, can cause dark pigmentation in the body.
\includegraphics[width=0.5\linewidth]{57a.png}
Which one or more of the following statements is/are correct?

• A. The character state "pigmentation" is homologous between species 1 and 3.
• B. The character state "pigmentation" is homologous between species 1 and 4.
• C. The character state "pigmentation" is not homologous for species 6 and 7.
• D. The character state "pigmentation" is not homologous between species 2 and 6.

Hint:

When analyzing phylogenetic trees, consider both the shared clade and potential evolutionary events that may lead to trait variations, such as gene mutations or silencing, to determine homology accurately.

Answer 1

The Correct Option is A, D

Step 1: Reevaluate Homology in Phylogenetic Context. Understanding homology requires assessing both the genetic and evolutionary context within which traits occur:
Species 1 and 3: Despite differences in pigmentation presence, their placement within the same clade suggests a shared evolutionary background for the trait.
Species 2 and 6: Although both lack pigmentation, their separate clade origins and potential genetic causes support non-homologous development.
Step 2: Conclusion Based on Phylogenetic Analysis. Homology of Pigmentation between Species 1 and 3: Supported by their common clade positioning and ancestral trait inheritance.
Non-Homology of Pigmentation between Species 2 and 6:Supported by their distinct clade origins and differing genetic influences.