# GenCh20answers - divided by the number of individuals mean...

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Quantitative Genetics 1. There are many traits that vary more or less continuously over a wide range. For example, height, weight, shape, color, reproductive rate, metabolic activity, etc., vary quantitatively rather than qualitatively. Continuous variation can often be represented by a bell-shaped curve, where the “average” phenotype is more common than the extremes. Discontinuous variation describes the easily classifiable, discrete phenotypes of simple Mendelian genetics: seed shape, auxotrophic mutants, sickle-cell anemia, etc. These traits show a simple relationship between genotype and phenotype. 2. The mean (or average) is calculated by dividing the sum of all measurements by the total number of measurements, or in this case, the total number of bristles
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Unformatted text preview: divided by the number of individuals. mean = x = [1 + 4(2) + 7(3) + 31(4) + 56(5) + 17(6) + 4(7)] (1 + 4 + 7 + 31 + 56 + 17 +4) – = 564 / 120 = 4.7 average number of bristle/individual The variance is useful for studying the distribution of measurements around the mean and is defined in this example as variance = s 2 = average of the (actual bristle count – mean) 2 = 1 / 120 ∑ [(1 – 4.7) 2 + (2 – 4.7) 2 + (3 – 4.7) 2 + (4 – 4.7) 2 + (5 – 4.7) 2 + (6 – 4.7) 2 + (7 – 4.7) 2 ] = 0.26 The standard deviation, another measurement of the distribution, is simply calculated as the square root of the variance. standard deviation = s = 0.26 = 0.51...
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