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Genetics of quantitative traits

Genetics of quantitative traits. Traits can be: discrete (qualitative) – phenotypic classes continuous (quantitative) – phenotypic range. Can be based on one or many genes. usually based on many genes plus the effects of the environment. Quantitative variation.

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Genetics of quantitative traits

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  1. Genetics of quantitative traits Traits can be: discrete (qualitative) – phenotypic classes continuous (quantitative) – phenotypic range Can be based on one or many genes. usually based on many genes plus the effects of the environment.

  2. Quantitative variation

  3. Evidence: resemblance between relatives a fundamental technique in quantitative genetics Quantitative variation can be based on both genetic and environmental variation

  4. Quantitative variation can be based on both genetic and environmental variation Evidence: response to selection artificial selection • two ways to measure the genetic basis • of a trait: • resemblance between relatives • response to selection

  5. 0.50 0.25 0.00 What is the genetic basis to quantitative variation? How can discrete alleles be the basis of continuous variation? Snapdragons – incomplete dominance for flower color

  6. R1R2 R1r2 r1R2 r1r2 R1R2 R1R1R2R2 R1R1R2r2 R1r1R2R2 R1r1R2r2 6/16 4/16 1/16 0 R1r2 R1R1R2r2 R1R1r2r2 R1r1R2r2 R1r1r2r2 r1R2 R1r1R2R2 R1r1R2r2 r1r1R2R2 r1r1R2r2 r1r2 R1r1R2r2 R1r1r2r2 r1r1R2r2 r1r1r2r2 What is the genetic basis to quantitative variation? How can discrete alleles be the basis of continuous variation? Additive – each R allele adds the same amount to the phenotype R = “+” r = “0”

  7. What is the genetic basis to quantitative variation? Human skin color - at least 3 loci that affect the production of melanin Polygenic trait – based on more than one gene (locus)

  8. low nutrient environment high nutrient environment Quantitative variation can be based on both genetic and environmental variation Evidence: lack of resemblance between relatives • genetically similar individuals • (clone, inbred line, siblings, • monozygotic twins)

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