Question

The three-spined stickleback (Gasterosteus aculeatus) is an excellent model to study natural selection, population divergence, and gene flow. This is because after the last glaciation, marine sticklebacks rapidly colonized and adapted to freshwater habitats across the Northern Hemisphere. Gene flow among lake and river dwelling populations of three-spined sticklebacks have been extensively characterized in a number of published studies. Use the specific details below to answer each question about population genetics of G. aculeatus. There is a large population of sticklebacks in a lake in Norway. At the s locus, population allele frequencies in the lake are S = 0.75 and s = 0.25. Each generation, individuals migrate form the lake into a small stream that flows out of the south end of the lake at a rate of 1 individual out of every 50. In the stream population, researchers measure the allele frequencies to be s = 0.49 and s = 0.51.

If the migration rate remains constant and no other evolutionary forces are operating, how many generations will it take for the S allele to exceed 0.53 frequency in the stream population?

Answer 1

The question asks for the number of generations needed for the S allele frequency to exceed 0.53 in a stream population of three-spined sticklebacks, given a constant migration rate from a lake population.

Step-by-step explanation:

The question concerns the population genetics of Gasterosteus aculeatus (three-spined stickleback), specifically addressing how the allele frequency of the S allele will change in a stream population due to migration from a lake population. To predict the change in allele frequency, we would need to apply concepts of gene flow and the Hardy-Weinberg equilibrium. However, without a specific formula or model to determine the rate of allele frequency change per generation, we can't precisely compute the number of generations required for the S allele frequency to exceed 0.53 in the stream population. It is evident that migration is introducing the S allele into the stream at a rate of 2% per generation (assuming the migrant reproduces), but other factors like selection, genetic drift, and mutation rate are also important and are not considered here.

Based on the allele frequencies provided and assuming no other evolutionary forces at work, over time and with continued migration, the frequency of the S allele in the stream will increase, but we can't determine the exact number of generations needed for the S allele frequency to reach 0.53 without a more complex genetic model.