Try This at Home continued

tion 0, just use the same pool of ten individuals to make a new generation. If the proportion is different, then get more of the colors you need to form a new generation representing the colors you picked. This is generation 1, from which you will again pick ten individuals to form generation 2 and so forth until you have ten generations.

What you have done is simulate ten generations for a very small population of ten individuals. To visualize the result, you can plot the number of pieces of the three different colors on the y-axis of a graph as a function of the generation number on the x-axis, as shown for the two sample simulations in figure B.11.2 and in table 11.1. What happened to the numbers of different colors in your simulation? If this simulation was repeated, what might you expect?

Note in the example shown that sometimes one color can become predominant or even become the only color in the population. That is, if one color is eliminated, there is no way for that color to reappear in the population without mutation (which occurs at a very low rate) or migration. If this happened in a real population, it would mean that genetic diversity would dramatically decrease. A gene trait that is not highly represented in the original population can be eliminated, as in simulation #1 with purple, and even traits that are prevalent in the original population can disappear, as with green in simulation #2. Conversely, a rare trait can be the only one in the population, as with purple in simulation #2.

Table 11.1 Results from Two Simulations of Random Genetic Drift

Simulation #1

Table 11.1 Results from Two Simulations of Random Genetic Drift

Simulation #1

generation

#0

#1

#2

#3

#4

#5

#6

#7

#8

#9

#10

green

4

4

4

6

7

7

8

7

8

9

9

purple

1

1

2

1

0

0

0

0

0

0

0

orange

5

5

4

3

3

3

2

3

2

1

1

Simulation #2

generation

#0

#1

#2

#3

#4

#5

#6

#7

#8

#9

#10

green

4

3

4

3

4

2

2

1

1

0

0

purple

5

6

6

7

6

8

8

9

9

10

10

orange

1

1

0

0

0

0

0

0

0

0

0

Try This at Home continued

Figure B.11.2 Simulations of Random Genetic Drift. Each form of the gene is represented by colors of paper represented by different symbols on the graph. The frequency of different forms of the gene at each generation is shown. Though we began with the same proportion of the colors, just by random chance, the proportions of purple and orange are different. This is the founder effect. Then with each generation, because the population size is small, by random chance certain colors can predominate in the population or even be the only color in the population.

0 0

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