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Chapter 2

Chapter 2 & 8 / Lecture 3

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Life Sciences
Brett Beston

Chapter 28Saturday October 08 2011104 PMArtificial SelectionThe process of humans choosing certain varieties of an organism over others by implementing breeding favoring one variety over the otherBasically picking traits for both animals and plants that we find productive for our causesWe can pick for both behaviourand physical traitsTeosinte was the how the corn first looked then now we have artificially selected for the corn we know todayNatural SelectionSelective advantage of a traitAny trait that helps the individual survive in their environment and increases fitnessIf this trait is heritable then it will be passed down the generations in turn increasing its frequencyExample Hunting behavior amongst wolves group hunting or individual hunting If in group hunting the wolf acquires more food this trait increases fitness and in turn its frequency in the generationsConsidering an animals phenotype is representative of its hunting behavior then the phenotype is a result of its phenotypeIf an animal hunted in a group it got more food which in turn increased its fitnessThis huntinginagroup gene will increase in frequency therefore more animals will hunt in groupsGene variants are called allele which are passed down the lineHow does Natural Selection operateNatural selection operates on 3 conditionsVariationdifferent forms of the trait1Fitness consequencesthe trait must affect reproductive success2Inheritablea means to pass it to future generation3A fourth hidden condition is the scarcity of resourceswhich is always met4VariationThere must be a selection something Natural Selection can select betweenThings that cause variation areGenetic factors1Environmental factors2Phenotypic variance genetic varianceenvironmental varianceVVVpGE2Heritability broad senseH V V VggE2Heritability narrow sense H VVAPV additive genetic variance V consists of additive and nonadditive components AGeg dominance and other gene interactionsVdepends on both the magnitude of additive effects of alleles and allele frequencyAGenetic variance average amount of variance between genotypesEnvironmental variance average amount of variance between individuals within the same genotypeGenetic factorsVariation based on genetic factors can be caused in 3 waysMutation any change in the genetic structure automatically creating new variation in 1the populationDNA fails to replicate properlyiExternal factors radiationiiGenetic recombination in metaphase when chromosomes line up for crossing over 2Possible in sexually reproducing organisms LIFE SCI 2D03 Page 1
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