lecture_notes_11_16_07 - Traits that affect an individuals...

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1 Johanne Brunet Biocore 301, fall 2007, Population Genetics LECTURE summary for November 16, 2007 Lecture 3: Learning objectives Continue impact of non-random mating on gene and genotype frequencies (see lecture notes for lecture 2 section on non random mating). Introduction to Selection Definitions Evolution: change in gene frequencies over time Selection: a mechanism by which evolution can occur Adaptation: change in a population with favorable characteristics accumulating over generations Selection Selection acts on phenotypes; Response to selection depends on additive genetic variance; Narrow sense heritability matters for selection; Artificial and natural selection; Conditions necessary before natural selection can occur : - Limited resources - struggle for existence: organisms produce more offspring than environment can support; Variation in traits among individuals; Heritable traits;
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Unformatted text preview: Traits that affect an individuals survival and/or reproduction. Natural selection Natural selection is the differential success in reproduction and survival that results from the interaction between individuals that vary in heritable traits and their environment Differential success in reproduction results in certain alleles being passed to the next generation in greater proportions than others. Modes of selection Directional selection: selection for one of the extreme of a trait; changes the mean of a trait. Selection for higher crop yield Disruptive selection: selects for both extremes. Changes mean and increases the variance; Selection for beak lengths in Darwin finches Stabilizing selection: does not change the mean, decreases the variance of a trait. Selection for baby body weight in humans...
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This note was uploaded on 04/29/2008 for the course BIOCORE 301 taught by Professor Howell during the Fall '07 term at Wisconsin.

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