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BIOL 1001 (162)
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Chapter 4

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York University
BIOL 1001
Tamara Kelly

Chapter 4 Evolution change in allele frequencynatural selection acts on individualsevolutionary change occurs in populationsPopulation group of individuals from the same species that live in the same area and regularly interbreed natural process is not the process that causes evolution4 mechanisms that shift allele frequencies in populations1Natural Selection increases the frequency of certain allelesthe ones that contribute to reproductive success in a particular environment2Genetic Drift causes allele frequency to change randomly In some cases drift may cause alleles that decrease fitness to increase in frequency3Gene Flow occurs when individuals leave one population join another and breed Allele frequencies may change when gene flow occurs because arriving individuals introduce alleles to their new poplations and departing individuals remove alleles from their old populations4Mutation modifies allele frequencies by continually introducing new alleles The alleles created by mutations may be beneficial or detrimental or have no effects on fitnessnatural selection is not the only agent responsible for evolutioneach of the 4 evolutionary processes has different consequencesChapter 41Approach to study the four evolutionary processes1Biologists create mathematical models that predict the fate of alleles over time under various conditions2They collect data to test the predictions made by the models3They apply the results to solve problems in human genetics conservation of endangered species or other fields 1908 beliefThe changes in allele frequency occur by the random fusion of gametes simply as a result of sexual reproductionmeiosis followed by the random fusion of gametes egg and sperm to form offspringSome biologists claimed that dominant alleles inevitably increase in frequency when gametes combine at random Others predicted that two alleles of the same gene inevitably reach a frequency of 05Hardy and Weinberg tested these hypotheses by
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