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23 Cards in this Set
- Front
- Back
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Consequences of Loss of Genetic Diversity |
Genetic drift, Population Bottlenecks, Founder Effect Leading to: decreased individual fitness, decreased population size, decreased rate of evolution (evolutionary rate correlated w/ population's genetic variability) (decreased variability vessels ability of population to evolve in response to changing environment) |
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Goals of conservation biology (relative to genetic diversity) |
Short term- days to decades; prevent local extirpation and global extinction mid-term- decades to millennia; preserve potential for evolution by natural selection long-term- millennia or more; preserve potential for future speciation |
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Levels of Genetic variation |
Within an individual Among individuals within a population Among population |
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Genetic variation within individuals |
Heritable variation coded in genes Gene- specific region of DNA coding for proteins, RNA, and regulates gene expression ---Monomorphic- single form (allele) ---Polymorphic- 2 or more alternate forms (alleles) At a gene locus, indivs could be heterozygous or homozygous |
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What is..? Heterozygous/Homozygous Heterozygosis Genetic Variation |
Homo- 2 copies of same allele Hetero- 1 copy each of 2 different alleles Heterozygosis- proportion of gene loci for which individual is heterozygous. common measure of genetic variation. -Genetic variation is sum of alleles in all individuals of a population. Can be measured by mean individual heterozygosity |
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Genetic variation among populations |
-Species rarely exist as single interbreeding population (panmixia) -Species populations show genetic variation from: Random factors: Genetic drift, population bottlenecks, founder effect Nonrandom factors: natural selection Population Divergence: Ht= Hp + Hpt |
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Population Divergence Formula |
Population Divergence: Ht= Hp + Dpt Ht= total genetic variation (heterozygosity) Hp= avg divergence within pops Dpt= avg divergence among pops |
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Factors affecting genetic variation among populations |
Mutation Genetic Drift Gene Flow Natural Selection Effects all four influenced by effective population size (Ne)-- # of breeding individuals -Ne smaller than census population size (N) because not all indivs equally capable to breed |
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Mutation |
Increases genetic diversity. can be Neutral- most mutations are Deleterious- few. Accumulation can lower fitness and increase probability of extinction Beneficial- very few. |
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Fixation |
Fixation- all individuals of population homozygous for the (deleterious) allele -Probability of fixation of deleterious allele increases with decreasing population size. Especially because of inbreeding, relatives will share deleterious allele. -May lead to Mutational Meltdown (fixation lowers fitness and survival of indivs, and pop declines, more likely other deleterious alleles become fixed, etc. |
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Genetic Drift |
Random fluctuation of gene frequencies of time due to change -Decreases genetic diversity. Without mutation/ gene flow, genetic drift leads to : ---Fixation of one allele ---Elimination of other alleles Implications: some alleles may not be passed by chance alone to next generation, reducing genetic diversity. more likely in small pop. |
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Demographic bottlenecks Gene Flow |
Population size greatly reduced by catostrophic event, then recovers -Magnitude of genetic loss depends on size of bottleneck generation & growth rate after bottleneck -Gene flow is movement of genes across populations (increasing genetic div within a population, decreasing gen div among populations) ---Due to immigration/emigration ---not all migrants breed; migrants doesn't equal gene flow |
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Implications for Gene Flow |
One migrant per generation is necessary to maintain gene flow rate sufficient to minimize loss of heterozygosity and allow for local adaptation |
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Mate selection & Inbreeding Depression |
Mating is not random usually. Small populations may lead to inbreeding depression. -Leads to decreased individual fitness from increased frequency of homozygous genotypes -Due to expression of deleterious recessive alleles in homozygotes due to loss of heterozygosity -Physical/chemical barriers in plants and dispersal of one sex in animals help avoid inbreeding |
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Implications of Inbreeding Depression |
Result in decreased: -Metabolic Efficiency -Growth Rate -Reproductive output -Disease resistance >more severe in smaller populations >can be alleviated by outbreeding to mask deleterious alleles and increase heterozygosity >increased fitness of outbred, heterozygous offspring= heterosis or hybrid vigor |
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Implications of Outbreeding Depression |
Decreased individual fitness from gene flow among populations -Due to genetic swamping of locally adaptive genes -Due to breakdown of co-adapted "gene complexes" |
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Natural Selection |
Natural Selection- differential survival/ reproduction of diff genotypes in the population. Decreases gen div. :directional, and stabilizing (nonrandom) Occasionally maintains steady level of genetic diversity :disruptive selection |
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Directional Selection & Disruptive Selection |
Directional: Common when environment is slowly changing -One phenotype favored so frequency increase over time. Decreases gen var Disruptive: 2 extreme phenotypes favored over intermediate. frequency of 2 extremes both increase over time. Maintains gen var and may lead to speciation. |
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Stabilizing selection |
Intermediate phenotype favored over extremes so frequency increases over time. Decreases gen var |
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Identifying and prioritizing groups for conservation |
Every population is genetically distinct, but cannot all be conserved 1. What is appropriate unit for conservation? 2. What level of genetic uniqueness qualifies group for conservation action? |
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Evolutionary significant units (ESUs) |
Population characterized by: -Substantial reproductive isolation from other pops -Substantial evolutionary isolation from other pops |
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Genetic structuring within a species |
Species- collection of pops with hierarchical genetic structures based on genetic similarity (from geography and gene flow Phylogeography- Description of genetic/evolutionary structuring in geographic context -Implies that conservationists should preserve genetically diverse subset of pops (ex. genetic structure in the bowfin) |
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Conservation strategies based on phylogenetics |
Phylogenetic should be considered when prioritizing taxa for conservation 1.Conserve basal taxa 2.Conserve most unique taxa 3.Conserve speciose taxa 4.Conserve taxa that maximize phylogenic diversity |
