Morph B Dominance Explained

This question relates to population genetics, specifically the effect of mutation rates on the relative abundance of different morphs (forms) within a population.

Mutation Dynamics

We have two morphs, A and B, in a population. They mutate between each other:

• Morph A mutates to Morph B with probability $p_1$.
• Morph B mutates to Morph A with probability $p_2$.

The problem states that $p_1 \gg p_2$, meaning the mutation rate from A to B is significantly higher than the mutation rate from B to A.

Analysis of Morph Frequencies

Although both morphs reproduce at equal rates, the mutation process continuously converts morphs from one form to another.

• The forward mutation (A to B) occurs at a high rate ($p_1$).
• The reverse mutation (B to A) occurs at a very low rate ($p_2$).

This results in a net flow of individuals from morph A to morph B over time. The high rate of A converting to B, coupled with the low rate of B converting back to A, creates a strong 'mutation pressure' favoring morph B.

Conclusion

Because there is a constant and strong net conversion of morph A into morph B, morph B will tend to increase in frequency relative to morph A. Therefore, over time, Morph B will dominate the population.