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Lecture_04-01-23-2014

Lecture_04-01-23-2014 - Lecture 4 Quan-ta-ve Gene-cs...

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Lecture’4:’Quan-ta-ve’Gene-cs’
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Linking’genotype’to’phenotype.’ Gregor’Mendel’was’an’Augus-ne’ Monk’who’lived’in’Austria’in’1800s.’ Began’to’carry’out’many’experiments’ on’pea’plants.’ He’no-ced’that’if’you’cross’peas’with’ white’flowers’with’peas’with’purple’ flowers’all’the’oFspring’(±1)’would’ have’purple’flowers.’ When’he’crossed’the’±1’(produce’±2)’ most’of’the’oFspring’would’have’ purple’flowers,’but’some’would’have’ white’flowers’(3:1’ra-o).’
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PaQerns’of’Dominance’ Mendel’discovered’paQerns’of’dominance’in’pea’plants.’ Purple’flowers’are’always’dominant’over’white’flowers.’ PP’ Pp’or’ pP’=’purple’ONLY’ pp’=’white.’ Same’for’many’diFerent’traits’in’pea’plants’
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Simple’inheritance?’ There’are’many’traits’that’show’“Mendelian’ inheritance”.’ Including’eye’color’in’ Drosophila ’and’hair’color’in’mice.’ Many’human’gene-c’diseases,’cys-c’fbrosis,’ Hun-ngton±s’chorea.’ Most’traits’show’con-nuous’varia-on.’ We’cannot’assign’individuals’to’categories.’ Con-nuous’distribu-on’=’quan-ta-ve’trait.’
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Use’a’frequency’distribu-on.’ Many’quan-ta-ve’characteris-cs’exhibit’a’symmetrical’curve’ à ’normal’distribu-on.’ Two’other’common’types’of’distribu-on’are’skewed’and’ bimodal.’
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Extensions’of’Mendelian’Gene-cs’ We’can’use’Mendel±s’principles’to’test’how’many’genes’ seem’to’be’causing’varia-on’in’a’trait.’ Now’we±re’dealing’with’a’ codominant’trait!’F1s’do’not’ resemble’either’parent!’
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Influence’of’the’environment’ The’influence’of’the’environment’is’ especially’clear’in’a’study’on’height’ in’Yarrow’Plants.’ Three’plants’are’iden-cal’ gene-cally’(cuDngs).’ Grown’at’three’diFerent’eleva-ons.’ Huge’diFerences’in’height’en-rely’ due’to’environment.’
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Measuring’quan-ta-ve’traits:’The’variance’ The’variance’of’a’trait’is’a’key’sta-s-c’that’tells’us’how’ much’a’trait’varies’within’a’popula-on.’ Variance’(s 2 )’is’calculated’by’Frst’es-ma-ng’the’mean’ (average)’of’a’popula-on’for’a’trait’of’interest.’ Need’a’representa-ve’sample!’ Then’calculate’how’far’the’samples’deviate’from’the’ mean.’ Then’square’those’devia-ons’and’divide’the’sum’of’ squares’by’the’number’of’individuals’sampled.’ The’higher’the’variance,’the’more’varia-on’there’is’in’ the’sample.’
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