You are to manipulate a two-allele, multi-generational, STOCHASTIC model of a population evolving under the influence of genetic drift. This model should allow you to assess the impact of population size on the magnitude of drift, and the likelihood of fixation.
Give you additional practice with MS Excel and quantitative reasoning.
List the different micro evolutionary processes covered in the course and contrast how they change allele frequencies over time. Apply population genetic equations to explore evolutionary processes.
This exercise will give you the opportunity to solidify your understanding of genetic drift now that we have covered the subject in lecture. The Excel file has already been set up to contain a single population of 50 individuals. You are to use copy/paste (with some editing) to add four additional populations to the graph (total of 5 pop’s). Starting with p0 = 0.5 you will collect data for 100 populations of size 50 by hitting the F9 key 19 times (20 total x 5 pops=100 pops). F9 causes Excel to recalculate, and the spreadsheet calculation is based, to some extent, on a random number. Record how many of those 100 populations fix for each of the p and q alleles (table below). Select a representative graph for screen-grabbing to turn in with this assignment. Then repeat this process with p0 = 0.1.
Next, copy the contents of this page to the N=30 worksheet and delete off the last 20 individuals (i.e., you are reducing N to 30). Make sure your graph is using data from this new page, and not the N=50 page, otherwise you will not see increased drift effects (see Select Data after right-clicking inside the graph). Again, generate the 100 populations of data for p0 = 0.5 and p0 = 0.1 and record the outcomes. Again, screengrab a representative graph.
Finally, copy the contents of this page to the N=10 worksheet and delete off the last 20 individuals (i.e., you are reducing N to 10). Again, make sure your graph is using data from this new page, and not the N=30 page. And again, generate the 100 populations of data for p0 = 0.5 and p0 = 0.1 and record the outcomes. Again, screengrab a representative graph.
- Contrast how the three different populations (p0 = 0.5) evolve over time. Include reference to your three, representative graphs in your answer.
- Based on your data does the frequency of an allele determine its likelihood of fixation due to drift? Explain, with reference to the data you collected.
