FA2011lecture21

FA2011lecture21 - typically in uenced by multiple genes as...

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Unformatted text preview: typically in uenced by multiple genes as well as environment exhibit continuous variation rather than discrete phenotypes a trait controlled by 3 genes with semi-dominant alleles acting additively is hard to distinguish from one controlled by 30 genes! With a normal distribution: 67% of scores fall within 1 S.D. of the mean 96% within 2 S.D 99% within 3 S.D distribution of ear lengths obtained from a parental ear of 11 cm: mean: standard deviation: variance: indicates how much of the variance is due to genetic factors inbred lines >>> homozygous at every locus: AA BB CC DD etc. Cross two different inbred lines together: AA BB CC DD.... X aa bb cc dd.... All offspring Aa Bb Cc Dd... not inbred but still genetically uniform (every F1 has same genotype!) But if you cross two of these F1s together, get independent assortment and many, many different genotypes not at all genetically uniform. H 2 = V g /V t (where V t = V g + V e ) variety 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 P60 4 21 24 21 8 P54 3 12 15 26 15 10 2 F1 1 12 12 14 17 9 4 F2 2 5 6 12 18 17 17 10 6 4 2 X = 7.1 V = 1.2 (V e only) X = 16.9 V = 2.0 (V e only) X = 12.1 V = 2.3 (V e only) X = 12.9 V = 4.8 (V t ) indicates how much of the variance is due to genetic factors...
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FA2011lecture21 - typically in uenced by multiple genes as...

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