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Lecture 12

Lecture 12.docx

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Biology 1001A
Tom Haffie

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October 25, 2011 Chapter 17.1-17.2 (Lecture 12) 17.1- Variation in Natural Populations • Phenotypic traits exhibit quantitative or qualitative variation within populations of all organisms. These discrete differences are called polymorphisms • Genetic variation, environmental factors, or an interaction between the two cause phenotypic variation within populations. Only genetically based phenotypic variation is heritable and subject to evolutionary change • Genetic variation arises within populations largely through mutation and genetic recombination. Artificial selection experiments and analyses of protein and DNA sequences reveal that most populations include significant genetic variation 17.2- Population Genetics • Population- a group of individuals of a single species that live together in the same place and time • All the alleles in a population comprise its gene pool, which can be described in terms of allele frequencies and genotype frequencies • To recognize a population that may be evolving we need a null model (reference point), describing what we’d expect if evolution were NOT occurring o The Hardy-Weinberg Principle is a null model that defines how evolution does not occur • Hardy-Weinberg Principle- in the absence of evolutionary forces, allele frequencies remain unchanged over time, and genotype frequencies are predictable from allele frequencies o It is a mathematical model that describes how genotype frequencies are established in sexually reproducing organisms. o According to this model, genetic equilibrium is possible only if all of the following conditions are met: 1. No mutations are occurring 2. The population is closed to migration from other populations 3. The population is infinite in size 4. All genotypes in the
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