​Synonymous mutations (solid black circle) and non-synonymous mutations (different symbols) are plotted on two hypothetical phylogenies (A and B) given below.​

​The phylogenies above may represent the following types of selection - positive, negative or neutral. Which one of the options given below gives the correct combination of the types of selection observed in phylogenies A and B?​

Correct option is A

Key points:

• Synonymous mutations (solid black circles) do not change the amino acid sequence (often neutral).

• Non-synonymous mutations (different symbols) change the amino acid sequence and may be subject to selection (positive or negative).

Interpreting phylogenies:

• Phylogeny A:

  • Synonymous mutations (black circles) are more frequent than non-synonymous mutations.

  • Non-synonymous mutations are rare or absent.

  • This pattern indicates that non-synonymous mutations are being removed or suppressed.

  • This is typical of negative (purifying) selection, which removes deleterious mutations.

• Phylogeny B:

  • Non-synonymous mutations appear frequently.

  • Synonymous mutations are relatively less frequent or equal.

  • Frequent non-synonymous mutations suggest that amino acid changes are tolerated or favored.

  • This is typical of positive selection, which favors advantageous mutations.

Correct option:

1. A shows negative selection, B shows positive selection