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Lecture

Biol 121- 2010.03.15- Evolution- Allele Frequencies in Populations (Ch. 25).docx

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Department
Biology
Course
BIOL 121
Professor
Carol Pollock
Semester
Winter

Description
Biol 121 225 Freeman 503508 511520Mar 15 10 Allele Frequencies in Populations Population a population is a group of individuals from the same species that live in the same area at the same time and interbreed Population genetics population genetics looks at contribution of alleles to a population quantification of genetic variation in a population measurement of changes in a population over timeevolution Four mechanisms that shift allele 1 Natural selection increases frequency of certain allelesthe ones that frequencies in populations contribute to success in survival and reproduction2 Genetic drift causes allele frequencies to change randomly and in some cases drift may even cause alleles that decrease fitness to increase in fq3 Gene flow occurs when individuals leave the population and join another and breedAllele frequencies may change when gene flow occurs bc arriving individuals introduce alleles while departing individuals remove alleles4 Mutation modifies allele frequencies by continually introducing new allelesthe alleles created by mutation may be beneficial detrimental or have no effect on fitnessnatural selection is not the only agent responsible for evol each of these four processes have diff consequences natural selection is the only mechanism that acting alone can result in adaptation the other three mutation gene flow drift do not favour certain alleles over others mutation and drift introduce a nonadaptive component into evol Agrostis tenuis growing on heavy A tenuis is a plant species and some of its individuals can grow on heavy metals on an abandoned mine in metals such as in an abandoned mine site in Walesthe population has Wales adapted and evolution has occurred therefore a change in allele frequency has occurred Gene pool all the gametes of a single generation in a population can put all the genes together in a pool and calculate the expected frequency of particular alleles if pulled out gametes at random p and q pfrequency of dominant allele qfrequency of recessive allele qfrequency of homozygous recessive 2pqfq of heterozygous pq1 p22pqq21 HardyWeinberg HW principle or HW describes a nonevolving population equilibrium ie The frequency of alleles and genotypes in the gene pool remain constant sexual recombination through meiosis and random fertilization do not change the populations genetic structure Assumptions of HW theorem 5 1 No natural selection at the gene in question no advantage of an allele 2 No genetic drift random change in allele frequency 3 No gene flow immigrationemigration0 4 No mutation no new alleles 5 Random mating no sexual selection Limitations of HW theorem 2 1 Assumptions above 5 are rarely true in a natural population 2 Usually the allele frequency changes from one generation to the next Applications of HW theorem 2 1 Modelingbeing able to predict the allele frequencies 2 Null modelworks as null hypothesisif not met then evol is occurring 1
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