A population of finches lives on an island some distance from the mainland, where another population of finches of the same species resides. In both populations, the size of the birds' beaks is influenced by two alleles at the beak locus, B and b. Finches with the BB genotype have the largest beaks, bb have the smallest beaks, and Bb individuals have a beak size intermediate between the two homozygotes. On the island, the frequency of the B allele is 0.3, and the frequency of the b allele is 0.7. On the mainland, both alleles are equally frequent (0.5).
(a) If the migration rate from the mainland to the island is 0.1 (meaning that 10% of individuals in the island population migrate in from the mainland every generation), what is the change in the frequency of the B allele on the island in one generation due to migration? Assume there is no migration from the island back to the mainland.
(b) The genotypes at the beak locus have the following fitness on the island: wBB = 0.95, wBb = 0.98, wbb = 1. Which allele is the most fit? What size beak is selectively favored on the island? What do you predict will happen to the frequencies of these alleles in the long term?
(c) The island experiences a severe drought for two consecutive years, which kills a plant species on the island that makes small seeds eaten by the finches. As a consequence, the food available decreases and the average size of edible seeds on the island increases greatly. Birds with large beaks are much better able to crack large seeds and thus better able to survive the drought. Which allele is the most fit? How do you predict the allele frequencies of B and b will change during this drought?
A population of finches lives on an island some distance from the mainland, where another population of finches of the same species resides. In both populations, the size of the birds' beaks is influenced by two alleles at the beak locus, B and b. Finches with the BB genotype have the largest beaks, bb have the smallest beaks, and Bb individuals have a beak size intermediate between the two homozygotes. On the island, the frequency of the B allele is 0.3, and the frequency of the b allele is 0.7. On the mainland, both alleles are equally frequent (0.5).
(a) If the migration rate from the mainland to the island is 0.1 (meaning that 10% of individuals in the island population migrate in from the mainland every generation), what is the change in the frequency of the B allele on the island in one generation due to migration? Assume there is no migration from the island back to the mainland.
(b) The genotypes at the beak locus have the following fitness on the island: wBB = 0.95, wBb = 0.98, wbb = 1. Which allele is the most fit? What size beak is selectively favored on the island? What do you predict will happen to the frequencies of these alleles in the long term?
(c) The island experiences a severe drought for two consecutive years, which kills a plant species on the island that makes small seeds eaten by the finches. As a consequence, the food available decreases and the average size of edible seeds on the island increases greatly. Birds with large beaks are much better able to crack large seeds and thus better able to survive the drought. Which allele is the most fit? How do you predict the allele frequencies of B and b will change during this drought?
