ANT 120

Lab 1: The Forces of Evolution

There are four mechanisms that can lead to evolutionary changefrom one generation to the next: mutation, natural selection, geneflow, and genetic drift. In this laboratory exercise we willexamine the action of genetic drift andnatural selection. The key difference betweenthese two mechanisms, which can be difficult to get a handle onwithout direct experimentation, is that natural selectionprivileges some individuals over others on the basis of theirbiological traits while genetic drift privileges some individualsover others with no regard to their biological traits.

Data Table for Genetic Drift Experiment

	Frequency of black beetles (alleles)
Generation	0	1	2	3	4	5	6	7	8	9	10
Round 1	0.5	0.5	0.6	0.6	0.5	0.4	0.6	0.8	0.9	0.8	0.7
Round 2	0.5	0.4	0.4	0.5	0.3	0.2	0.2	0.3	0.1	0.0	0.0

Data Table for Natural Selection Experiment

	Frequency of black beetles (alleles)
Generation	0	1	2	3	4	5	6	7	8	9	10
Green Forest	0.5	0.5	0.5	0.4	0.2	0.2	0.3	0.3	0.2	0.1	0.0
Black dirt	0.5	0.6	0.6	0.7	0.8	10.0	10.0	10.0	10.0	10.0	10.0

Using the data, answer the questions on the other side of thissheet.

Questions

1. Compare the results from the genetic drift experiments to thenatural selection experiments. Are there any clear differences inthe results? If so, what is the reason for the differences?

2. In cases where one of the colors of beetle was eliminated,how could the allele for this color re-enter the population? Whichforces of evolution would be required?

3. From these experiments, how might genetic drift and naturalselection affect natural populations of organisms differently? Ifthe population of beetles was 20,000 instead of 20 (and 10,000survived each generation) how would this influence the effects ofgenetic drift vs. natural selection?

4. Is the outcome of genetic drift or natural selection morepredictable? How might these different mechanisms of evolutionarychange relate to functional traits of organisms?