ch. 25 - Chapter 25 Quantitative genetics and...

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Chapter 25: Quantitative genetics and multifactorial traits Objectives: Understand how the interaction between the environment and genes in phenotypes is estimated (calculated). Understand how to calculate estimates of genotype and environmental variance in heritability. Understand how to calculate the narrow-sense heritability in artificial selection. Understand the usefulness in studying twins to distinguish nature from nurture. Understand the role of markers in QTL mapping. Definitions Discontinuous variation - phenotypic data that fall into at least two distinct non-overlapping classes. Ex.) tall and dwarf plants, red and white eye color. Continuous variation - phenotypic variation from quantitative traits distributed from one phenotypic extreme to another in an overlapping or continuous manner. Ex.) Height and weight within the human population. Quantitative or polygenic inheritance - phenotypes that result from the additive effects of many genes.
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Meristic traits - phenotypes recorded in whole numbers. Thephenotypes do not have an infinite number of possibilities. Threshold traits - phenotypes with a small range of discrete possibilities but the cause is due to multiple factors (polygenic, environment, diet etc.) Chronic diseases T2D.
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Multiple Gene Hypothesis for Qualitative Inheritance - When red crossed with white a pink grain was produced so…incomplete dominance. - F2 did not produce expected 3:1 ratio, instead 15:16 red variation and 1:16 white. Four shades of red occurred. - since incidence was in 16ths then 2 genes each with 2 alleles responsible. Additive - P1 AABB and aabb . The AABB alleles are additive towards color while aabb alleles are not. - F1, 2 additive A B alleles and 2 non-additive alleles a b , thus the intermediate color (pinkish). - F2 off-spring may have 4, 3, 2, 1 or 0 additive alleles. The intensity is proportional to the number of additive alleles and each contributesto the total amount of pigmentation produced by the grain.
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Calculating the number of polygenes or quatitative trait loci For a small number of phenotypes: 2n + 1 rule where 2n + 1 is the total number of possible phenotypes and where n = the number of additive loci . Ex) n=4, then 9 possible phenotypes
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This note was uploaded on 10/07/2009 for the course BIOLOGY 2203 taught by Professor Anthwal during the Fall '08 term at Temple.

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ch. 25 - Chapter 25 Quantitative genetics and...

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