ch. 27 - Chapter 27: Population genetic (cont'd) (Things...

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Natural selection The non-random differential reproduction or survival of genotypes. Important force in evolutionary change. Fitness - an individual organism’s genetic contribution to future generations. The reproductive success or survival of 1 genotype compared with the reproductive success or survival of other genotypes in the population. Remember that fitness depends on the phenotype so if 2 different genotypes have the same phenotype then they will have the same fitness. Changes in fitness results when a phenotype influences survival and reproduction. Fitness is represented by w and refers to a specific genotype and its value ranges from 0 to 1. A value of 1 indicates that all the individuals survive and reproduce. Whereas a value of 0.2 indicates that only 20% of these individuals will survive and reproduce. Chapter 27: Population genetic (cont’d) (Things that affect the Hardy Weinberg equilibrium)
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Genotypes: AA Aa aa X offspring (mean) 10 5 2 To calculate fitness for each genotype take the mean number offspring produced by a genotype and divide it by the mean number of offspring produced by the most prolific genotype: Fitness ( w) w AA = w Aa = w aa = A related variable is the selection coeeficient ( s ) which is the realtive intensity of selection against a genotype. The selection coefficient is 1- w . The selection coefficient for the preceding 3 genotypes are: AA Aa aa S (1-w) s AA = 0 s Aa = 0.5 s aa = 0.8 10 10 10 5 10 2
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Changes in allelic frequency due to selection AA Aa aa Initial genotype frequencies p 2 2 pq q 2 Fitnesses w AA w Aa w aa Proportionate contribution of genotypes to pop. p 2 w AA 2 pq w Aa q 2 w aa Relative genotype frequency after selection p 2 w AA 2 pq w Aa q 2 w aa w w w (Mean fitness w = p 2 w AA + 2 pq w Aa + q 2 w aa )
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Alcohol is a common substance in rotting fruit and fly larvae use the enzyme Alcohol Dehydrogenase (ADH) to detoxify the effects of the alcohol. In some fruit flies two alleles are present at the locus that encodes ADH; ADH F and ADH S . Female fruit flies with different ADH genotypes produce the following numbers of offspring when alcohol is present. Genotype
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ch. 27 - Chapter 27: Population genetic (cont'd) (Things...

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