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The bottleneck and founder effects commonly cause populations small enough for genetic drift to be significant Genetic Drift Random changes in allele.

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Presentation on theme: "The bottleneck and founder effects commonly cause populations small enough for genetic drift to be significant Genetic Drift Random changes in allele."— Presentation transcript:

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2 The bottleneck and founder effects commonly cause populations small enough for genetic drift to be significant Genetic Drift Random changes in allele frequency. Will occur faster in small populations NOT the same as Natural Selection (which is not random)

3 Large pool Small pool AAAa aaAAAa aa AAAa aa AAAa aa AAAa aa AAAa aa AA Aa aa AAAa aa AA Aa aaAAAa aa AAAa AA Aa aa AAAa AAAa aa AAAa aa AA Aa aa AA Aa aa AAAa aa AA Aa aa AAAaaa Genetic drift faster in small population

4 Changes in allele frequencies In small populations, genetic drift operates quite quickly and new alleles can increase in frequency by chance.In small populations, genetic drift operates quite quickly and new alleles can increase in frequency by chance. In larger populations, genetic drift is slower, and natural selection is more important in increasing the frequency of a new allele.In larger populations, genetic drift is slower, and natural selection is more important in increasing the frequency of a new allele.

5 Founder Effect Small group of individuals move away from the main population. Eg a group of insects blown by wind to a small island Bottleneck Effect Catastrophic events wipe out many individuals. Eg avalanche, volcanic eruption

6 Original large population has equal proportions of blue and red A small founder population may be separated from the parent population

7 AA Aa AA A catastrophe wipes out most of the parent population Aa AA Aa AA Aa Parent population has a single mutant Mutant has established in the new population

8 Genetic drift RANDOM RANDOM CHANGES IN GENE POOL Occurs over time Faster in small populations Without other factors Genetic drift will eventually lead to the extinction of one allele RESULT: Change in allele frequencies

9 Founder & Bottleneck effects Founder effect – small population of pioneers Bottleneck effect – small population due to catastrophe + Founder effect and bottleneck effect both cause an immediate change in allele frequency + small population is more prone to genetic drift RESULT: Change in allele frequencies


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