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c)Do some of the mechanisms work against each other? How? Make predictions about future genetic variation (more homozygous/ heterozygous) within a population based on drift/gene flow/natural selection/mutation. Do the same for genetic variation among populations.i)Natural selection: I’m assuming natural selection should occur in all situations. Beak length increases in bugs when they feed on bigger seeds. Other examples include selection for resistance to antibiotics, against bright coloration by guppy predators, and changes in beak 8
length in Darwin’s finches. Selection can also produce clines over largedistances. For natural selection to occur: there must be (1) Variation(2) variation must be heritable(3) Some individuals survive and reproduce better than others(4) Differential survival and reproduction not based on chanceii)Genetic drift: Genetic drift decreases genetic variation. Drift is when allele freq. in population is changed by chance. Effects small populations the most. Gene frequencies fluctuate randomly until one allele is fixed (not necessarily the “most fit” allele). Genetic drift increases homozygosity within populations, but produces divergence between populations (clumping kinda?)(1) Two major mechanisms lead to small population size(a) Founder effect (small number of colonists)(i)Some lizards from big island get stuck on small island thus creating a new population. Greater homozygosity in population and divergence among populations. (b) Bottlenecks (dramatic reductions in numbers)(i)Biting flies knocked down lion population to a few males. By chance, most of those males had double headed sperm. Bottle neck example. iii)Gene flow: Migration of individuals among populations, Opposes effects of drift: more variation within populations and fewer differences between them. Metapopulations occur when a species is fragmented and dispersal (and gene flow) occur between them (may prevent local extinction)(1) Ex. Mosquitoes and pesticide resistance(2) Lizards from the big island get stuck on anew smaller island but there are bridgesbetween the smaller islands. Fixation isnot as easy here. Movement is easier.Fewer fixed alleles, more genetic variationof each island opposed to genetic driftexample. Gene flow gives greaterheterozygosity in population and differentpopulations are more similar. iv)Mutation: Rare-1 in every million copies. Must enter germ line to be heritable. While it is the origin of genetic variation, it is so rare that its impact on population evolution is small. Genetic recombination much more common way to get varied traits.4)Give several examples of evolution in natural populations, pointing out what phenotypes are under selection and the selection mechanism.a)With Darwin’s finches, after a drought the average beak size in the population had increased. They adapted to eat the larger drought-tolerant seeds through the mechanism of natural selection.