Effects of Genetic Drift (2 of 2)

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The impact on small populations:
The marble-drawing scenario also illustrates why drift affects small populations more. Imagine that your bag is only big enough for 20 marbles (a tiny bag!) and that you can only draw four marbles to represent gene frequencies in the next generation. Something like this might happen:

Impact on small populations

Notice how quickly and drastically the marble ratio changed: 1:1, 1:3, 0:1.

The same process operates in small populations. All populations experience drift, but the smaller the population is, the sooner drift will have a drastic effect. This may be a big problem for endangered species that have low population sizes.

Explore further
•  Sampling error and evolution
•  Bottlenecks and founder effects

Teach this!
Lesson plans for teaching about genetic drift

Next Topic:
Natural Selection

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