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BIO207H5 (42)
Chapter 5

Chapter 5 Notes.doc

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Fiona Rawle

Chapter 5Quantitative GeneticsPRINCIPAL POINTSDiscontinuous traits exhibit few distinct phenotypescontinuous or quantitative traits display a range of phenotypesContinuous traits have a range of phenotypes many loci contribute to phenotypeenvironmental factors influence the phenotype producedby a genotypecan be studied by using samples of populati hygonsstatistics such as1Mean2Variance3Correlations between characterscombined with analysis of varianceregression analysisvariation can be partitioned into geneticenvironmental componentsbroadsense heritability of a trait is the proportion of the phenotypic variance resulting from genetic differences among individualsnarrowsense heritability is proportion of the phenotypic variance due only to additive genetic variance both measures depend on particular population in certain environmentamount that a trait changes in one generation as a result of selection on the trait is called the response to selectionmagnitude of the response to the selection depends on the selection differentialnarrowsense heritabilitygenetic correlations arise when 2 traits are influence by the same genes or linked genestrait is selected genetically correlated traits also exhibit a response to selectionQuantitative trait loci determine continuous traits can be identified through markerbased mappingQTL mapping provides estimate of the numberrelative importance of genes influencing quantitative genetic variationThe Nature of Continuous Traits1Most traits studied havebeen characterized by presence of only few distinct phenotypesseed coats of pea plants either grey or white seedpods either green or yellowplants either tall or shortin each trait phenotypes were markedly differenteach phenotype is easily separated from all other phenotypestraits with few distinct phenotypes are called discontinuous traitsDiscontinuous traitssimple relationship exists between genotypephenotypewhen dominance occurs the same phenotype is produced by 2 different genotypessingle genotypes can give rise to range of phenotypes as the genotype interacts with variable environments during development to give rise to norm of reactiontraits exhibit only few distinct phenotypesdescribed in qualitative termsContinuous traitsthere are not many traits with phenotypes that fall into a few distinct categoriestraits like human birth weight adult height protein content in cornnumber of eggs laid by Drosophila exhibit wide range of possible phenotypestraits with a continuous distribution of phenotypesphenotypes of continuous traits must be described in quantitative measures which are known as Quantitative Traits field of quantitative genetics studies inheritance of these traitsQuestions Studied in Quantitative Geneticsgreat deal of genetic variationamount of variationhow its distributed determines populations genetic structurequantitative genetics plays important role in understanding of evolution conservationcomplex human traitsespecially important in agricultural genetics where traits such as crop yield rate of weight gain milk productionfat content are all studiedpsychology uses it to study IQ learning abilitypersonalityhuman geneticists use it to study traits such as blood pressure antibody titer fingerprint patternsbirth weightindividuals different tin the quantity of a traitquantitative geneticists would ask1To what degree does the observed variation in phenotype result from differences in genotypeto what degree does this variation reflect the influence of different environments2How many genes determine the phenotype2
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