Evolution Assignment for 10/14 - Using models to explore the consequences of genetic drift and migration

Go to the class website either through Moodle or the Biology Department web page. Select “Assignments and instructions” and then click on “More evolution simulations.”

Select “Genetic Drift and Migration”

What you see:

· A graph of the number of simulated populations (N=32) with a particular frequency of an allele (A1).

· P = 0 at the left end of the X-axis and 1 at the right end of the X-axis.

· At the start of the simulation, all 32 populations have a frequency of 0.5.

What you can change:

· N = the size of each population (all are of equal size)

· Mu = the migration rate (not the “mutation” rate as written in the simulation). This is equivalent to the proportion of individuals moving out of a population, randomly apportioned among the other populations.

· The number of generations of change (each click of the “iterate” button cycles through ten generations)

Questions

1. Starting with no migration (m = 0), and N = 25, iterate 20 times (200 generations). Describe the distribution of p-values among populations.

2. What does this mean with respect to overall genetic variability in the species (considering all populations, combined)? How much variability is seen, on average, within each population?

3. Now repeat the process of “1” but with N = 250. Compare these results to those obtained when you specified smaller population sizes.

4. Reset N to 25, and set migration to be 0.1, and then iterate the system 20 times. Describe the distribution of p values. How does migration affect the pattern of variability among populations?

5. Reset the system by clicking on “m” to set it at 0.1 (this is the same set of parameters as for question 4). When you repeat the 20 iterations do you see exactly the same pattern? Why?s