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Lecture 09&10 - DIRECTIONAL SELECTION One allele is...

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BIOLOGY 1001: LECTURES 9 & 10 GENETIC STRUCTURE OF POPULATIONS; THE GENETIC BASIS OF MICROEVOLUTION Gene frequency - The proportion of a particular allele among all alleles at a gene locus. Causes of change in gene frequency: 1.Mutation - A change in the nucleotide sequence whether by substitution, duplication, insertion or deletion. 2.Gene flow - The migration of genes into a population from other populations by interbreeding. 3.Genetic drift - The random change in frequency of alleles in a population, especially when population size is suddenly reduced to a few individuals. 4.Natural selection - Differential survival and reproduction of individuals carrying particular heritable traits. RELATIVE FITNESS: The contribution of one genotype to the next generation compared to alternative genotypes at the same locus. SELECTION COEFFICIENT: Difference in relative fitness between two genotypes.
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Unformatted text preview: DIRECTIONAL SELECTION: One allele is favored over another, resulting in the virtual elimination of the inferior allele. Factors permitting the coexistence of alternative alleles: 1.Alternatives are selectively neutral 2.Stabilizing selection: heterozygote advantage (overdominance) 3.Disruptive selection: heterozygote disadvantage 4.Frequency-dependent selection: an allele confers a selective advantage only when rare HARDY-WEINBERG THEOREM Predicts the frequency of genotypes in a population, assuming: 1.Individuals mate at random with respect to genotype 2.Gene frequencies remain constant 3.Individuals carry only two alternative alleles, A and a First measure allele frequencies within the population with: p = frequency of allele A 1-p = q = frequency of allele a Then the frequency of each genotype in the next generation will be: AA = p 2 Aa = 2pq aa = q 2...
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