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Unformatted text preview: Concepts from Lecture 21 Causes of microevolution Genetic Drift – This is basically a sampling problem. If the population is too small, by chance only some alleles will get passed down and some will get lost. See the Slide 10 for example of the population fixing on the red allele. Remember Violating HW means the population is evolving (changing over time) – so losing an allele or even just changing the allele frequency over time is violating HW. If the population is small then chances of the SAMPLING (reproduction) of the population not correctly matching the true frequency of alleles is greater. This is the point of the simulations on slides 7‐9. The fertilization lottery is the chance than an individual passes on its alleles to the next generation. So if we simplify it to just what is the frequency of an allele (A) followed through successive generations we can see that an allele can be lost much more readily if the population is small (40 individuals, panel A) than when it is larger (400 individuals). The bottleneck effect is the drastic reduction in population size that reduces the variation in a population. This is an extreme event when the number of individuals shrinks and so by chance variation will be lost because only a few individuals had the chance to pass along to the next generation. The founder effect is similar to bottleneck except that few individuals leave a population and go on to start a new population. This means that only the variation present in those individuals is what will be in the start of the new population and this would typically be a much reduced set of alleles. Natural Selection – this is accumulation and maintenance of favorable genotypes in a population. Natural selection operates on PHENOTYPE but what is passed on to children is GENOTYPE. Evolutionary Fitness – contribution that an individual makes to the gene pool of the next generation relative to the contribution by others. Relative Fitness is contribution of a genotype to the next generation gene pool, compared with the contributions of alternative genotypes for the same locus. Absolute fitness average number of viable, fertile offspring produced by an individual with that phenotype (a particular genotype). Relative fitness – average contribution of individuals with one phenotype (genotype) to the next generation relative to the contributions of alternative phenotypes (genotypes). ...
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This note was uploaded on 08/15/2010 for the course BIO 5c taught by Professor Zhu/cardullo/rao during the Spring '08 term at UC Riverside.
- Spring '08