Genetic Drift

Genetic Drift: Random change in allele frequency causes an allele to become more common or less common.

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Example: T=Tall, t=Short (T:t)

5:7

Only The Three Circled Giraffes Leave Offspring

5:5

Only The Two Circled Giraffes Leave Offspring

10:0

Now The Only Allele Present Is The Tall (T) Allele

Gene Pool and Allele Frequency

Gene Pool: The total variety of genes and alleles present within a population at a given point in time.

Allele Frequency: How common an allele is in a population (e.g. B:b = 10:6).

Example:

Gene Pool = Only Short-Necked Giraffes

A New Long-Necked Comes Along (Immigration)

He Adds New Genes/Alleles To The Gene Pool

Now The Giraffes Can Reach The Trees

Yay!

EVOLUTION

...Or They Would've Turned Into Cows

This evolution would increase the population of giraffes because there is more food for them to eat (tree leaves) and less competition with other animals for grass.