Chapter 24 1.28.08

Chapter 24 1.28.08 - Chapter 24 1 Honors Biology Book Notes...

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Chapter 24 1 Honors Biology Book Notes Chapter 24 – Evolutionary Process 1/28/08 - Evolutionary Process o Population : a group of individuals from the same species living in the same area that regularly interbreed Natural selections occur on individuals, but evolution takes place only in populations o 4 Allele-Shifting Mechanisms (1) Natural Selection – increases the frequency of certain alleles, the ones that contribute most to reproductive success Only mechanism which consistently results in adaptation (2) Genetic Drift – causes allele frequencies to change randomly, sometimes even causes alleles that decrease fitness to increase (3) Gene Flow – occurs when individuals enter or leave a population & allele frequencies may change when this occurs due to new alleles introduced by incoming individuals and alleles removed by emigrating individuals (4) Mutation – modifies allele frequency by introducing new alleles that better, worsen, or don’t do anything to fitness o Mutation, gene flow, genetic drift do not favor alleles, rarely produce adaptation - Scientific approach to studying populations – (1) create mathametical model that tracks fate of alleles over times (2) Collect data to make predictions on model (3) Apply results to solve problems o Gene pool : term coined by Hardy & Weinberg to analyze consequences of matings among all individuals of a population – assumed all gametes produced in each generation go into bin called gene pool o Allele frequencies are unitless numbers between 0 – 1 that represent percentage of that allele in pool, together must add up to 1 Represented by letters q and p o Hardy-Weinberg Principle : claims that (1) if frequencies of allele A 1 and A 2 in a population are represented by p and q, then frequency of genotypes A 1 A 1 , A 1 A 2 , A 2 A 2 will be given by p 2 , pq, q 2 for generation after generation and (2) when alleles are transmitted according to rules of Mendelian inheritance, their frequencies do not change over time so other factors must come into play if evolution is to occur o None of 4 mechanisms of evolution may act if Hardy-Weinberg principle is to hold true o 5 Conditions of Hardy-Weinberg Principle (1) No natural selection at gene in question (2) No genetic drift or random allele frequency changes affecting gene in question [no random change due to sampling effect]
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Chapter 24 2 (3) No gene flow, so no new alleles were added by immigration or lost by emigration (4) No mutation (5) Random mating, so mates did not choose each other o If all 5 conditions apply, then genotypes A 1 A 1 , A 1 A 2 , A 2 A 2 will have proportions p 2 , pq, q 2 and no evolution will occur o In a sense, Hardy-Weinberg principle is a null hypothesis [what you
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Chapter 24 1.28.08 - Chapter 24 1 Honors Biology Book Notes...

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