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Evolution - Mechanisms of Evolution Reading:Freeman Chapter...

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Mechanisms of Evolution Reading:Freeman, Chapter 24 For additional info, this is an excellent lecture on evolution-I borrowed at least on pls . atu . edu /biology/biology/people/ bisk / genbio /ch16_lecture. ppt
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Review: Mechanisms of Evolution The basic assumptions of the Hardy- Weinberg equilibrium; no mutation no migration random mating no natural selection infinite population size
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The Mechanisms of Evolution Mutation Allele (gene) flow Selection Genetic Drift Nonrandom mating each one is, in essence, the result of a violation of one or more of the assumptions of the Hardy-Weinberg equilibrium
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Mutation A mutation is a change in the organism’s DNA. Mutations may affect somatic (nonreproductive tissue), or they may affect the germ line (reproductive tissue). Except in clonal organisms, somatic mutations cannot generally be passed on. Evolutionary biologists are interested in heritable mutations , the kind that can be passed on to the next generation. A heritable mutation changes one allele into another, sometimes creating an allele that is not already present in the population.
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Some mutations create dominant alleles, some create recessive or codominant alleles. Some mutations are harmful or lethal, many are totally neutral-they have no effect, a few are favorable. Whether a mutation is harmful, neutral, or favorable, depends upon its environment
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Cat Mutations
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Songbird mutations
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Mutations are random events : their occurrence is independent of their selective value - i.e., they do not occur when they are needed any more often than they would otherwise. Mutations at any single locus are rare events : mutation rates at a typical locus are about 1 in 10 6 gametes.
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Since each individual has thousands of alleles, the cumulative effect of mutations is considerable: Consider that each of us has about 3.5x10 4 loci, and the mutation rates are about 1x10 -6 per locus, thus, about 1 in 30 of our gametes has a new mutation somewhere in its genome. That means about 7% of us are mutants, more or less. YOU could be a mutant.
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Mutations are the ultimate source of genetic variation Mutations are the only source of new alleles (other than the occasional transfer of alleles by viruses). Mutation is thus the ultimate source of genetic variation…it creates the raw material upon which natural selection acts.
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Example-an interesting mutation: In humans, one interesting mutation is called the CCR- δ 32 allele (the locus is named CCR, it is one of many alleles at that locus) This allele codes for a 32 base pair deletion that makes the protein nonfunctional. Lacking this protein on the surface of their blood cells, homozygous individuals (it is effectively codominant) are essentially resistant to HIV-HIV cannot infect their cells.
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