Chapter 24 Evolutionary Processes

Chapter 24 Evolutionary Processes - Chapter 24 Evolutionary...

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Chapter 24: Evolutionary Processes -Evolution is a change in allele frequencies over time. -Evolution is cause by: 1) natural selection —increases the frequency of certain alleles that leads to reproductive success. 2) genetic drift —random allele change. (can sometimes increase alleles that decrease frequency) 3) gene flow —when one immigrates into or emigrates from a population. (introduces and removes alleles from the population) 4) mutation —continually introduces new alleles. (can be beneficial, detrimental, or have no effect on fitness) -Only natural selection consistently causes evolution. The other 3 don’t favor certain alleles so they rarely result in adaptation. (Also, mutation and gene flow are non-adaptive components of evolution) I. The Hardy-Weinberg Principle (Analyzing change in allele frequencies) a. Tests what happens to the genotype of an entire population (as opposed to just two parents with a specific genotype for punnett squares) b. Gene pool —A collection of all of the gametes produced in each generation. To find out what genotypes would be in the next generation, H & W chose gametes out of the gene pool randomly. This gives you the genotype of the offspring and the frequency of each group. c. Disproved that the dominant allele does not always increase in frequency and the trend of both alleles does not go towards 0.5 d. 2 important claims of the H-W principle: i. 1) If A 1 = p and A 2 = q then A 1 A 1 = p 2 A 1 A 2 = 2pq A 2 A 2 = q 2 (these are H-W proportions) ii. 2) If alleles are passed down following Mendalian genetic rules, there much be another factor for evolution to occur (the 4 things in intro) e. If no evolutionary mechanism is acting on the population and random mating occurs, then genotypes should be in H-W proportions. If they are not in those proportions, there is an evolutionary mechanism taking place or non-random mating. f. Just because it follows H-W number doesn’t mean it never had an evolutionary mechanism affecting it. It means that currently there is none. g. H-W is the Null hypothesis i. Null hypothesis = observation when the hypothesis being tested is wrong. Biologists want to test which evolutionary mechanism is occurring, and the H-W is used as the null. h. Look at examples in book: MN blood types and HLA genes in humans i. Calculation steps for seeing if its under H-W: 1
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1. Given genotype frequencies or the numbers of various genotypes 2. Calculate observed allele frequencies 3. Calculate observed genotype frequencies using H-W principle 4. Compare observed and expected genotypes (if the numbers are alike or almost
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This note was uploaded on 03/30/2010 for the course BIO 1005 taught by Professor Nef during the Spring '10 term at Holy Family University.

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Chapter 24 Evolutionary Processes - Chapter 24 Evolutionary...

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