Presentation on theme: "Genetic Drift Random changes in allele frequency."— Presentation transcript:
1 Genetic Drift Random changes in allele frequency. Will occur faster in small populationsNOT the same as Natural Selection (which is not random)The bottleneck and founder effects commonly cause populations small enough for genetic drift to be significant
2 Genetic drift faster in small population Large poolSmall poolAAAaaaGenetic drift faster in small populationAAAaaaAAAaaaAA
3 Changes in allele frequencies 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.
4 Founder Effect Bottleneck Effect Small group of individuals move away from the main population. Eg a group of insects blown by wind to a small islandBottleneck EffectCatastrophic events wipe out many individuals. Eg avalanche, volcanic eruption
5 Original large population has equal proportions of blue and red A small founder population may be separated from the parent population
6 Mutant has established in the new population AAAAAAAAAAAAAAAAAAAAAaAAAAAaAaAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAaAAAaAAAaAaAAAaAAAAAAAAAAAAAAAAAaAAAAParent population has a single mutantAAAaAAAaAAAAAAAAAAA catastrophe wipes out most of the parent populationAaAaAAAAAAAAAAAa
7 Genetic drift RANDOM CHANGES IN GENE POOL Occurs over time Faster in small populationsWithout other factors Genetic drift will eventually lead to the extinction of one alleleRESULT: Change in allele frequencies
8 Founder & Bottleneck effects Founder effect – small population of pioneersBottleneck effect – small population due to catastropheFounder effect and bottleneck effect both cause an immediate change in allele frequency + small population is more prone to genetic driftRESULT: Change in allele frequencies
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