evolution4 (2) - Evolutionary Processes Mechanisms of...

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Evolutionary Processes
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Mechanisms of Evolutionary Change Evolution is defined as a change in allele frequencies over time. Natural selection acts on individuals, but evolutionary change occurs in populations. Adaptation is not the same as acclimation Genotype vs. phenotype
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The Importance of Genetic Diversity Evolution cannot occur without genetic diversity since there would be no variation for natural selection to act on. Genetic diversity itself is an important adaptation.
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Years since infected with HIV Percentage of HIV-infected people still alive 100 80 60 40 20 0 0 18 16 14 12 10 8 6 4 2 HETEROZYGOUS At MHC (major histocompatibility complex) loci HOMOZYGOUS At MHC Loci Sickle cell anemia!!
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Increasing Diversity is a Theme in Evolution Meiosis, sexual reproduction, and the diversity of eukaryotes. Meiosis makes eukaryotic sexual reproduction possible. Meiosis reduces the diploid chromosome number to haploid and introduces genetic variability through crossover and independent assortment. Note: no new alleles are created, only different combinations on any particular chromosome.
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Increasing Diversity is a Theme in Evolution Meiosis, sexual reproduction, and the diversity of eukaryotes. Meiosis makes eukaryotic sexual reproduction possible. Fusion of haploid gametes from two parents creates genetically different offspring, some of which may be more resistant to environmental changes and pathogens than the parents.
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Increasing Diversity is a Theme in Evolution Meiosis, sexual reproduction, and the diversity of eukaryotes. Meiosis makes eukaryotic sexual reproduction possible. The effect of potentially debilitating mutations is lessened since only half of the daughter cells of meiosis will receive a particular mutant allele.
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Parent Asexual reproductio n Meiosis Normal allele Defective allele Only half of the gametes have the defective allele. All offspring have a copy of the defective allele. Outcrossing Self-fertilization Only half of the offspring have the defective allele. Only 3/4 of the offspring have the defective allele.
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