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