6a. Five hundred years have now passed since planet Nerdsville 65A27-g was colon
ID: 82141 • Letter: 6
Question
6a. Five hundred years have now passed since planet Nerdsville 65A27-g was colonized by the astronomy club. As human populations tend to do, the inhabitants of Nerdsville 65A27-g have depleted their natural resources and severely polluted the only body of fresh water on the planet, Lake Shiticaca. Three islands occupy the middle of Lake Shiticaca, and are populated by the Greater Brown Sewer Lizard. These lizards used to swim from island to island, effectively homogenizing the allele and genotype frequencies of each island subpopulation, but the pollution in the lake is now so toxic that these lizards are no longer able to make the swim, and the subpopulations have become completely isolated. As part of their quarter research project, the students of the University of Nerdsville population biology course construct bridges between the islands to re- unite the Greater Brown Sewer Lizard subpopulations. Given the following allele frequencies in each of the three subpopulations, and a migration rate (m) of 0.1 per generation, use the island model of migration to calculate the frequency of allele q in each subpopulation after 10 generations of migration. [hint: the average frequency of q in the migrants into population A is equal to the frequency of this allele in subpop's B + C, divided by 2]
Population A: q = 0.4 Population B: q = 0.2 Population C: q = 0.3
6b. What has been the impact of migration on these 3 populations with regards to the frequency of the q allele?
Explanation / Answer
Using the island model of migration,
Proportion of migrants moving into the island population each generation, m = 0.1
As per the hint, the frequency of q allele among the migrants coming into subpopulation A is equal to the frequency of this allele in subpopulations B+C/2.
So, qeq = 0.2+0.3/2 = 0.25 (frequency of allele q at equilibrium)
Now, frequency of q allele in subpopulation A after 10 generations of migration
q' = q-qeq(1-m)+qeq
q' = 0.4-0.25(1-0.1)+0.25
= 0.15(0.9)+0.25
q' = 0.385
Frequency of q allele in subpopulation B after 10 generations of migration
q' = q-qeq(1-m)+qeq
= 0.2-0.25(1-0.1)+0.25
= 0.205
Frequency of q allele in subpopulation C after 10 generations of migration
q' = q-qeq(1-m)+qeq
= 0.3-0.25(1-0.1)+0.25
= 0.295
B. After generations of migration between the three subpopulations, the frequency of allele q will become average between the initial frequency and the equilibrium value.
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