Before a power plant went on-line in Providence Harbor, 1000 killifish (Fundulus

Question

Before a power plant went on-line in Providence Harbor, 1000 killifish (Fundulus heteroclitis) of known electrophoresis genotypes were placed in an experimental enclosure: 40 FF, 320 FS and 640 SS individuals (F stands for fast migrating protein allele, S = slow migrating allele in gel electrophoresis). Two weeks after the power plant began operation and used harbor water in the cooling towers, the 680 fish that were still alive were collected and analyzed for genotype, with the following results: 40 FF, 256 FS and 384 SS. (i) What are the allele frequencies after selection? (ii) Determine the relative fitnesses of each genotype and the selection coefficient against each genotype. (hints: Think about fitness as the percentage of each genotype that survives the heat stress (e.g.

Explanation / Answer

(i) The allele frequencies after selection are: Total population: 680 FF = 40 = q2 Hence q = 6.3. SS = 384 = p2. Hence p = 19.4 FS = 256 = 2pq. The correct value of 2pq is 2 x 6.3 x 19.4 = 244.4 which is close to the real value. ----------------------------- (ii) Before heat stress: The relative fitness of each genotype is: RF of qq is 40/960 = 0.04 RF of pq is 256/744 = 0.34 RF of pp is 384/616 = 0.62 After heat stress: The relative fitness of each genotype is: RF of qq is 40/640 = 0.06 RF of pq is 256/424 = 0.6 RF of pp is 384/296 = 1.2 ----------------------------------------------------- The selection coefficient of the three genotypes after heat stress is: s = 1-W[Relative fitness] For qq genotype: s = 1-0.06 s = 0.94 For pq genotype: s = 1-0.6 s = 0.4 For pp genotype: s = 1-1.2 s = - 0.2 The relative fitness of each genotype is: RF of qq is 40/640 = 0.06 RF of pq is 256/424 = 0.6 RF of pp is 384/296 = 1.2 ----------------------------------------------------- The selection coefficient of the three genotypes after heat stress is: s = 1-W[Relative fitness] For qq genotype: s = 1-0.06 s = 0.94 For pq genotype: s = 1-0.6 s = 0.4 For pp genotype: s = 1-1.2 s = - 0.2

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