Lecture 23 - Quantitative Genetics the study of the genetic...

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Quantitative Genetics – the study of the genetic basis of continuously varying traits. Bract Color in Indian Paintbrush
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Frequency Histograms - a statistical distribution that shows the number of individuals vs. a measure. Distribution Function – a continuous curve that is an idealized representation of the actual distribution.
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Statistical Measures sued to describe Quantitative traits: 1) Measures of Central Tendency a) Mean = average = x b) Mode = most frequently observed class 1) Measures of Dispersion a) Variance = average squared deviation of the observations from their mean = s2 b) Standard Deviation = Square root of the Variation = s
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How do you know there is a genetic basis for the variation? The Mean of the F 3 progeny more closely resembles that of the sampled parental types than the overall mean – responds to selection P F 1 F 2 F 3 Clearly not a 1:2:1 ratio Increased Variance relative to F 1 Petal Length in Nicotiana longiflora Mean of the two parental lines Possible Incomplete Dominance?
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Phenotypic Distributions For Specific Genotypes For a Population
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Convert a Quantitative trait into a Mendelian trait: Controlled environment What makes a Quantitative trait a QT is that the phenotypic variance between genotypes is smaller than the phenotypic variance between individuals of the same genotype.
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Effect of Gene Numbers Wilhelm Johannsen 1857-1927 Coined terms Gene, genotype, and phenotype Generated 19 inbred lines of beans from same pop. with seed weight varying from 0.35 to 0.64g. Each line had a distinct and heritable weight. If seed weight is controlled by single allele pair Aa In breeding would produce: AA and aa; only two genotypes.
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