Evolution 4

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Author:
Chloe
ID:
7507
Filename:
Evolution 4
Updated:
2010-02-20 22:00:20
Tags:
migration natural selection genetic drift
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Description:
migration, natural selection, genetic drift
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  1. migration
    • movement of alleles between populations
    • results in gene flow: transfer of alleles from the gene pool of one population to another
    • can increase genetic variation within populations
    • tends to decrease variation between populations
  2. models describing migration
    -continent island
    -island
    -stepping stone
    -isolation by distance
    • -continent island: moving from mainland to bare islands
    • -island: all islands exchange equally
    • -stepping stone: populations next to eachother are exchanging equally
    • -isolation by distance: more migration to closer populations
  3. genetic drift
    -2 types
    • chance or random event that influences evolution
    • effects are immediate and cummulate over time
    • larger effect on smaller populations
    • with times, drift changes allele frequencies no matter what the population size is
    • founder event: moving from big population to smaller, allele frequencies are not the same, lose diversity
    • bottle neck: a few individuals contribute genes to the entire future population of the species, one type survives better due to luck- not because they are better
  4. rate of fixation
    • depends on population size
    • eventually all populations would fixate, but migration (gene flow) doesnt let that happen
  5. genetic diversity
    • effected by population size
    • needed to adapt to changing environments
  6. patterns of natural selection
    • directional (purifying)- homozygote advantage, over time favored allele frequency will equal 1 (fixed), reduces diversity, disadvantageous allele lost over time
    • stabolizing- favores intermediate variants and acts against extreme phenotypes, heterzygote advantage, balencing selection (keeping both in population)
    • diversifying- selects against phenotypes near the average value, favoring extreme phenotypes, can lead to speciation (new species), difficult to get populations to diverge
  7. varying selection
    • temporal fluctuation: different phenotypes favored in different generations
    • multiple niche polymorphism: if you have the allele you survive, intermediates tend not to survive to adulthood
    • frequency dependent selection: kind of balancing selection, results in maintenance of polymorphism
    • ---inverse (rare is good): side mouth sucking fish, the rare one can find more food
    • ---positive (common is good): whatever alleles present are determined by evolutionary standpoint (mimcry)

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