Question

Water snakes are common in the area around Lake Erie. They live onthe mainland as well as islands in the lake. The island andmainland populations are relatively isolated, but migration doesoccur. Interestingly, selection favors banded water snakes on themainland and unbanded on the islands. Bandedness is controlled byone locus with two alleles: banded (B1) and unbanded (B2) withbanded being dominant.

Each generation, some proportion of snakes migrates from themainland to the island. On the island, the frequency of B1 is verylow (0.2). On the mainland it is much higher (0.9). Only 12% of themainland individuals migrate successfully to the island. Aftermigration, random mating occurs (no sexual selection). Eachpopulation then returns to HW equilibrium in the next generation,and selection occurs before the next bought of migration. Theselection coefficient against banded water snakes on the island is0.15 and it is 0 for the unbanded water snakes. What is thefrequency of B1 after migration and selection?