Biology 32: Evolutionary Biology
Getting started with Allele A1, 2010
Selection: Use AlleleA1 to model various selection regimes by reconstructing Figure 6.12 from your textbook
(p. 184 and see below). How will you do this? Use relative fitness values that are between 0 and 1.
Reset to the default parameters by selecting the Reset button. Make allele A1 slightly deleterious (s = 0.05)
and dominant. What relative fitness values did you use & what will happen to the frequency of allele A1?
Select the Multiple button to compare the above scenario with the following… Change the relative fitness
values such that allele A2 is slightly deleterious (s = 0.05) but recessive. What will happen? Can you say
anything meaningful about the rate of evolutionary change between the two scenarios?
Mutation: There are 2 boxes in AlleleA1 that let you control the mutation rate. One controls the mutation
rate from allele A1 to allele A2, while the other controls the mutation rate from allele A2 to allele A1. Note that
the mutation rates must be numbers between 0 and 1.
Return to the default parameters by pressing the Reset button, and then change the number of generations to
1000 and one of the mutation rates to 0.0001. What do you predict will happen? Were you correct?
Hit the Multiple button & select a different line color. Then change the mutation rate by an order of
magnitude in either direction. What do you predict will happen compared to the first run?
Finally, select a third color. Now change the mutation rate so that the value is an order of magnitude different
from the original value (0.0001), but in the opposite direction from last time. Summarize what happens
given these various levels of mutation.
Gene flow: AlleleA1 uses the one-island model of migration described in your textbook on pp. 225-227. The
simulation tracks the frequency of the A1 allele in the island population.
The parameter called Fraction of migrants each generation determines the number of individuals that move
from the mainland to the island every generation, as a fraction of the island population. For example, setting
the parameter to 0.1 means that each generation 10% of the individuals in the island population are new arrivals
from the mainland source population.
The parameter called Frequency of A1 in the source pop’n determines the frequency of A1 on the mainland
and by extension among each generation’s migrants.
Try the following simulation... Reset to the default parameters by selecting the Reset button. Then change
the following parameters: Frequency of A1 in the source pop’n = 0.8 and Fraction of migrants each generation
= 0.01 Make a prediction about what will happen. Does this make sense?
Next, hit the Multiple button & select a different line color. Then change only the Fraction of migrants each
generation (to 0.05). How is this scenario different from the first & does the graph make?
Finally, select a third line color & change the frequency of the A1 allele in the island population to 0.95.
Before you hit Run, what do you think will happen? Run the simulation – Were you correct? In general,
what does gene flow do to populations?