CH 23&24 LECTURE 5,6,7 AND 8
CH 23&24 LECTURE 5,6,7 AND 8 2570
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This 4 page Class Notes was uploaded by Austin Horner on Monday February 16, 2015. The Class Notes belongs to 2570 at Washington State University taught by Asaph Cousins & Raymond Lee in Winter2015. Since its upload, it has received 81 views. For similar materials see Bio 106- Organismal Biology in Biology at Washington State University.
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Date Created: 02/16/15
Genetic variation makes evolution possible The HardyWeinberg equation can be used to test whether a population is evolving Natural selection genetic drift and gene ow can alter allele frequencies in a population Z w rl39 c U1 3 D n 5quot o 3 L7 rl39 D o 3 lt 3 D n 3 m 3 U 3 rl39 m rl39 constantly causes adaptive evolution Natural selection acts on individuals but only populations evolve Genetic variations in populations contribute to evolution Discrete characteristics can be classi ed on an eitherorbasis Quantitative characteristics vary along a continuum within a population eye color height hair color mass Variation in genotype lead to variation in phenotype Not all phenotypic variation is heritable Natural selection can only act on variation with a genetic component Alternative versions of a gene two copies per diploid cell Proportion of alleles in a population Both copies of an allele are the same Each allele in a diploid are different Changes in the nucleotide sequence of DNA Mutations call new genes amp alleles to arise Only mutations in cells that produce gametes can be passed to offspring lSexual reproduction can shuf e existing alleles into new combinations Sexual recombination of alleles is more important than mutation genetically over time The study of how populations change The total of genes in a population at any one time Consists of all alleles at all gene loci in all individuals of the population Describes a population that is not evolving Frequencies of alleles and genotypes in a population s gene pool remain constant from generation to generation Rarely met in nature Extremely large population size No gene ow no migrations No mutations Random mating No natural selection IFor diploid organisms the total number of alleles at a locus is the total number of individuals times 2 l2 Alleles for each homozvgous dominant individual 1 Allele for each heterozygous individual Same logic applies for recessive alleles Ilf there are 2 alleles at a locus P and 39Q are used to represent their frequencies The frequencies in a population will add up to 1 So PQ1 Describes a hypothetical population In real populations Allele and genotypic frequencies DO change over time Natural Selection Genetic Drift Gene Flow IA sudden change in the environment may drastically reduce the size of a population The gene pool may no longer be re ective of the original populations gene pool IOccurs when a few individuals become isolated from a larger population ICan affect allele frequencies in a population Genetic Drift is signi cant in small populations Genetic Drift causes allele frequencies to change at random Genetic Drift can lead to a loss of genetic variation within populations I Genetic Drift can cause harmful alleles to become xed Causes a population to gain or lose alleles Gene Flow tends to reduce differences between populations over time Accumulates and maintains favorable genotypes in a population Natural Selection increases the frequencies of certain genotypes Fitting organisms to their environment over generations hree modes of selection are Favors individuals at one end of the phenotypic range Favors individuals at both extremes of the phenotypic range Favors intermediate variants and acts against extreme phenotypes Natural Selection increases the frequencies of alleles that enhance survival and reproduction IAdaptive evolution occurs as the match between an organism and its environment Selection can act only on existing variations Evolution is limited by historical constraints Adaptations are often compromises Chance Natural selection and the environment interact
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