## The Importance of Variation # 3. Variation and Genetic Drift

Begin with a pitcher of M&Ms illustrating color variation:

 Color Number Frequency Yellow 70 16.6% Brown 50 11.9% Green 43 10.2% Blue 54 12.8% Purple 100 23.7% Orange 55 11.6% Red 49 13.1%

Randomly pour some into cups and have each team calculate the number (and frequency) of each color in their population sample:

 Color Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Yellow 9 8 3 3 5 2 Brown 7 6 3 2 5 3 Green 3 8 1 2 2 3 Blue 7 4 3 2 3 10 Purple 22 5 4 7 5 9 Orange 6 4 3 4 1 5 Red 6 5 2 2 3 4

Note that although purple was the dominant color (highest frequency) in the parent population, this is no longer the case in three of the subset populations. (Dominant color shaded for each group.) If you have only a small portion of a population, the frequency is often skewed and over time, the population will continue to move in a direction where the frequency increasingly varies from the parent population. This is referred to as Founders Effect and it is often found on islands where a small number of individuals form the start of a new population. In other words, evolution (change in frequencies) does not have to occur only with strong selection as we saw in the previous activity. Evolution can also be greatly influenced by the starting population, especially if that starting population is small.

#### More on Variation:

 Variation within a Population