Lec 5 Bild 3 2011 for Ted

Lec 5 Bild 3 2011 for Ted - BILD 3 Lecture 5: Evolutionary...

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BILD 3 Lecture 5: Evolutionary processes and genetic variation I. Gene flow II. Natural selection (another look) III. Sexual selection IV. Preservation of genetic variation V. Why natural selection can not make optimal phenotypes
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I. Gene flow - transfer of alleles into or out of a population as a result of the movement of fertile individuals or their gametes (e.g., pollen) - can alter allele frequencies in populations - reduces existing genetic differences among populations - counteracts loss of genetic variation caused by drift - can oppose natural selection and adaptation
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Gene flow can oppose natural selection and adaptation Example: Wind dispersed pollen carries genes for copper tolerance into areas where tolerance is not an advantage.
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Gene flow can oppose natural selection and adaptation Example: Mytilus edulis (mussel) has planktonic larvae that readily disperse. lap 94 is an allele that allows M. edulis to cope with highly saline conditions. Gene flow inhibits fixation of lap 94 to the east and other alleles to the west.
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BILD 3 Lecture 5: Evolutionary processes and genetic variation I. Gene flow II. Natural selection (another look) III. Sexual selection IV. Preservation of genetic variation V. Why natural selection can not make optimal phenotypes
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II. Natural selection (a closer look) Natural selection blends chance and sorting. chance - creation of new genetic variants by mutation sorting - differential survival of phenotypes (relative fitness) Selection is the only evolutionary force that increases the frequencies of alleles that provide a reproductive advantage
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Relative fitness: The contribution an individual makes to the gene pool of the next generation, relative to the contribution of other individuals in the population Fitness is determined by factors affecting both survival and reproduction. Selection acts on the phenotype of individuals. Selection acts indirectly on the genotype via how the genotype affects the phenotype. Simple models of selection consider the relative fitness of genotypes.
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Determined by survival and reproduction. Selection acts on the phenotype of individuals. Relative fitness:
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Determined by survival and reproduction . Selection acts on the phenotype of individuals. Relative fitness:
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Relative fitness: How can we figure out if a population is increasing in its fitness? Are beneficial alleles (ones that will increase an individual’s relative fitness) increasing within a population? We can use a simple model to measure a population’s fitness
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DIRECTIONAL SELECTION extreme phenotypes most fit changes population mean decreases variation
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Simple model of directional selection Diploid organisms with two alleles (A, a) A is dominant; a is recessive. 10% of recessive homozygotes (aa) die before contributing
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Lec 5 Bild 3 2011 for Ted - BILD 3 Lecture 5: Evolutionary...

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