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Conservation Genetics-Lessons from Population and Evolutionary Genetics PowerPoint Presentation

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Description : Check out this medical presentation on Genetics, which is titled "Conservation Genetics: Lessons from Population & Evolutionary Genetics", to learn about Conservation Genetics, the science of understanding how genetic issues affect the conservation and restoration of populations and species.

Tags : Genetics, Conservation Genetics, Population, Evolutionary Genetics

Published on : Aug 29, 2021 | Views : 309 | Downloads : 0

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Conservation Genetics: Lessons from Population & Evolutionary Genetics
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Definition Conservation Genetics: The science of understanding how genetic issues affect the conservation and restoration of populations and species.
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II. Major Issues (from Frankham 1995) Inbreeding depression Accumulation of deleterious alleles Loss of genetic variance in small populations Genetic adaptation to captivity and effect on reintroduction success -Fragmentation of populations -Taxonomic uncertainty (unique?, novel?, hybrid?, hybridize for successful reintroduction?) small population size
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III. Taxonomic Uncertainty Example: Dusky Sea Side Sparrow (Ammodramus maritimus nigrescens) Avise and Nelson 1989
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IV. Small Population Size -Most threatened/endangered species exist in Small Isolated Populations Must focus on consequences of small population size Gaston et al. 1997 (ECOGRAPHY) Newton 1997 (ECOGRAPHY)
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Genetic Consequences of Small Population Size: -Loss of Genetic Variation -Inbreeding Depression -Accumulation of Mutations All as a result of Drift and Fragmentation
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V. Drift History: Natural historians, including Darwin, noted that some variation among individuals would not result in differences in survivorship and reproduction
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e.g., Gulick, Hawaiian land snails exhibited great diversity of shell color patterns
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Changes in pattern across generations arises by chance Drift (population genetic translation- Wright): Evolutionary process by which allele frequencies change by accidents of sampling
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VI. Origin of Accidents of Sampling Assume diploid population with 2 alleles at a locus A with frequency p a with frequency q Zygote = union of 2 independent gametes or union of 2 independent events Thus genotype frequencies represent binomial probability distribution: (p + q)2 or AA= p2, Aa = 2pq, aa = q2
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Assume: finite population size (N) Zygotes are a sample of gametes: A or a with frequency p and q Thus random sampling process will introduce variation of allele frequencies across gernation of Variance of binomial: pq/N Diploid organisms: pq/2N Loss of Heterozygosity is proportional to 1/2N or 1/2Ne (Population Geneticists use Ne because loss of heterozygosity is often greater than the census number)
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Effect of sampling variation after many generations Change in allele frequencey of Drosophila melanogaster populations
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VII. Consequences of Drift: -allele frequencies fluctuate randomly -populations vary by chance -increase variation among populations -decreased heterozygosity in populations -increased homozygosity in populations -increased genetic relatedness in population -SELECTION NOT AS EFFICIENT NeS < ¼ then deleterious alleles and new deleterious mutations will become fixed by drift (more later)
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VII. Consequences of Fragmentation A. Wahlund Effect: All of the same consequences as Drift decreases heterozygosity within populations increases homozygosity within populations increases genetic relatedness within populations
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Natural History Examples of Fragmentation (From Hamrick and Godt) # of P Gst species (within population) (among pop) pollen dispersal animal 164 36 0.2 wind 102 50 0.1 seed dispersal gravity 199 30 0.3 wind 105 43 0.1 P = % of loci with > 2 alleles Gst = proportion of genetic variation distributed among pop. FRAGMENTATION  LOSS OF GENETIC DIVERSITY WITHIN POPULATIONS
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B. Further consequences of Fragmentation Allee Effect: As density decreases, ability to find mates also decreases e.g. Oostemeiger, Arnica montana, Netherlands Visitation rates in small and large populations: Small Large Large High Density Low Density
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IX. Consequences of Inbreeding A. Inbreeding depression
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Low High Heterozygosity Low High Extinction Rate
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B. Loss of Genetic Variation Lakeside Daisey (hymenoxys acaulis var. glabra) Last remaining population in Illinois Lakeside Daisey is Self Incompatible M. Demauro, 1994
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Number of Mating Groups
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Selection of D. melanogaster for resistance to ethanol fumes in Large vs. Small populations Generation Resistance (minutes) Weber, 1992 L = Large S = Small Consider response to global climate change!
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C. Mutation Accumulation NeS < ¼ 1. Fixation of ancestral mutations (From Lynch and Burger, 1995)
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2. Introduction of new mutations
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3. Extinction Risks Due to Mutational Meltdown R = Reproductive Rate; K = Carrying Capacity
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Consequences of Mutations for Small Populations Critically Depend on: Mutation Rate Distribution of Mutation Effects (all deleterious?)
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X. Genetic Manipulation to Counteract Small Population Size Purging of “bad” mutations Natural History Examples: Husband and Schemske, 1996
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Drift led to both the fixation and extinction of deleterious alleles
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Purging critically depends on genetic basis of inbreeding depression: Inbreeding depression: expression of recessive deleterious alleles in homozygous condition Dudash and Carr, 1998 Inbreeding depression due to recessive alleles
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B. Crossing Programs to Restore Genetic Variability Case Study: Fenster and Colleagues Chamaecrista fasciculata
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XI. Conclusion Small population size may lead to lower genetic fitness through fixation of deleterious alleles XII. Future Directions We Need: -Better estimates of mutation rates and effects -Field based experiments to determine if a population can be purged of deleterious mutations -Studies to quantify effect of adaptation to captivity -Better understanding of the genetic basis of adaptive differentiation