Random Genetic Drift

This next exercise demonstrates random genetic drift. As with the founder effect, drift is more evident with small populations because random chance has greater impact on small populations than on larger ones.

Begin with a large number of pieces of colored paper, let's say green, purple, and orange. We suggest at least 100 pieces, with 60 percent green, 20 percent purple, 20 percent orange. This is your original "genetic pool," wherein each different form of the gene is represented by a given color and each piece of paper represents an individual.

Then pick ten pieces of paper randomly (that is, blind, without regard to color) from this initial "genetic pool." This is generation 0. Keep track of how many of each color you have at each generation. Note that the chances are that you did not get the same proportion of colors as in the original "genetic pool" of six green, two purple, and two orange. This, again, is the founder effect. That is, just by chance, you might pick many more purple or orange pieces than is representative of the original pool, but, just as likely, you might not get any purple or orange.

Now, we will reproduce this population for a few generations. At "each generation," randomly pick a piece of paper from your small population of ten. After you pick, note the color, then return the piece of paper to the population of ten, mix the pieces of paper, and then pick another and note its color. Do this ten times so that you again have ten individuals. This process simulates the genes that are randomly passed onto the next generation. The number of different colors represented by these ten individuals may or may not be the same as the original 10 pieces. But now, these ten colors you picked will form generation 1. If the proportion of colors is the same as genera-

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