Evolution of Populations (Chapter 16)Please set up your notebook for Cornell notes.
DarwinFelt that variations in populations were important but did not understand how variations were passed from parent to offspringDarwin’s work was linked w/Mendel in 1930’s
Lead to discovery that natural selection works on genes in a population
Genetic VariationGene pool all the alleles and genes in a populationFrequency the number of times a particular allele appears in a population
Evolution is an y change in the frequency of alleles in a population
Sources of genetic variationSexual reproduction each parent passes on half of their genes so each offspring has a different combination of parental genesMutations random changes in DNA; leads to a change in phenotype (physical appearance)
Mutations can be good or bad
Single gene and polygenetic traitsSingle gene trait trait that has only two alleles
Widow’s peak dominant traitPolygenic trait a trait that is controlled by two or more genes
Height in humansTends to be a bell shaped curve
Evolution as genetic changeNatural selection doesn’t act on genes; rather is affects which individuals survive or die
Natural selection on single gene traits change gene frequency and lead to evolution
Natural selection on polygenetic traitsDirectional selection when individuals on one end of the bell curve have higher fitness
Leads to phenotypes on one extremeStabilizing selection individuals in the center of the curve have higher fitness
Leads to average phenotypesDisruptive fitness both extremes of the bell curve are selected for
Leads to phenotypes on both extremes of the curve
Genetic Drift a change in gene frequency due to chance
Founder effect a population has a change in gene frequency as a result of migration
Leads to new species speciation
Speciation usually occurs when a population becomes isolated
Reproductive isolation two populations cannot interbreed and produce fertile offspringBehavioral isolation two populations could interbreed but courting behaviors keep them from breedingGeographic isolation two populations are kept apart by geographic barriers like rivers, mountainsTemporal isolation two or more species breed at different times
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