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.
|