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2012-02-06 22:19:25
Chapter 25 26

chapter 25 and 26Wh
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  1. What is polygenic?
    many genes each exerting a relatively small effect
  2. what is genetic correlation?
    when selection favoring alleles for one trait causes a correlated but suboptimal change in an allele for another trait
  3. What is pleiotropy?
    single allele affects multiple traits
  4. Describe fitness trade offs.
    a compromise beween traits in terms of how those traits are adapted for the enviroment; selection acts on many traits at once; every adaptation is a compromise.
  5. What are the genetic constraints?
    genetic correlation, lack of genetic variation, and fitness trade off.
  6. What is natural selection?
    Increases the frequency of those alleles that contribute to reproductive successes in a particular environment.
  7. What is genetic drift?
    Causes alleles frequencies to change randomly (due to chance), occurs in every population. When random loss or fixation of an allele occurs, genetic variation is lost. Founder effect and genetic bottleneck.
  8. What is founder effect?
    Immigrants establish a new population; new population is likely to have different allele frequencies than the source population by chance
  9. What is genetic bottleneck?
    when high mortality strikes individuals at random; bottlenecked population likely to have different allele frequenceies than original populations by chance. Likely to have decreased genetic variation and increased genetic differences within populations.
  10. What is gene flow?
    when individuals leave one population, join another and breed; causes allele frequencies in two populations to be more alike
  11. What is mutation?
    modifies allele frequencies by continually introducing new alleles; random with respect to fitness; most often result in deleterious alleles; usually inconsequential in changing allele frequencies at a particular gene
  12. What is the ultimate source of genetic variation of mutations?
    crossing over and independent assortment creates new combinations; but only mutation creates new alleles
  13. What is directional natural selection?
    Changes the average value of a trait; tends to reduce the genetic diversity of population; fixation and loss is rare b/c directional selection is rarely constant throughout a species' range and through time. Fitness trade off may counteract. Intermediate phenotype is optimal.
  14. What is stabilizing natural selction?
    reduces the amount of variation in a trait; average value of a trait stays the same; very large and very small babies die
  15. What is disruptive natural selection?
    Forms two distince populations which may eventually form two new species; increases amount of variation in a trait
  16. What are the types of natural selection?
    directional, stabilizing, disruptive, balancing selection and sexual selection
  17. Describe balancing selection.
    Heterozygote advantage; genetic variation is maintained; no single allele has a distincte advantage and increases in frequency; balance among several alleles in terms of their fitness and frequency. Occurs when environment changes over time or frequency dependent seelction (rare alleles favored instead of rare ones)
  18. What are the two kinds of nonrandom mating?
    inbreeding and sexual selection
  19. Describe inbreeding.
    Only heterozygotes produce heterozygote offsprings, but only half the time. Effect is increase in homozygotes, lower fitness (inbreeding depression). Allele frequencies do not change; only genotype frequency changes; increases evolutionary change (increase the rate at which purifying selection eliminates recessive deleterious alleles from a population).
  20. What is the fundamental asymmetry of sex?
    • Pattern: females invest more in their offspring than males do
    • Process: eggs are more expensive than sperms.
  21. What is sexual selection? What are the two types of sexual selection?
    Sexual selection acts more strongly on males and causes certain alleles to increase/decrease in frequency and results in evolution. Female choice and male male competition.
  22. What are the requirements for Hardy Weinberg to take effect? What did it serve as?
    no mechanisms of evolution and mating has to be random. Served as a nul hypothesis for determining whether evolution is acting on a particular gene in a population; recombination alone does not alter gene frequency; some other factor has to occur
  23. How is speciation identified?
    Biological species concept, morphospecies, phylogenetic
  24. What is monophyletic group?
    An ancestral population plus all of its descendants
  25. What is synapomorphies?
    Monophyletic groups are identified by it. It is homologous traits inherited from a common ancestor that are unique to certain populations
  26. What is species on the tree of life?
    the smallest monophyletic group
  27. What are the types of allopatry isolation?
    Dispersal: population moves to a new habitat, colonizes it and forms a new population. Vicariance: physical barrier splits a widespread population into subgroups that are physically isolated from each other. Shrimps is closer to the sister species on the other side of the isthmus than ones on the same side.
  28. What is sympatric isolation (speciation)?
    due to genetic drift and selecton, one species becomes two. polyploidization, tetraploid and disruptive selection.
  29. What is polyploidization?
    Genetic isolation created by formation of polyploidy individuals (mutants with more than two sets of chromosomes) that can reed only with each other. Two types autopolyploidy: duplicate chromosomes from same species. allopolyploidy: gain duplicate chromosomes from different species due to hybridzation event.
  30. What is tetraploid?
    genetically isolated from wild-type because they produce diploid gametes rather than haploid gametes. Result would be triploid if the two gametes combined; triploid individuals have a dysfunctional set of chromosomes
  31. What is disruptive selection?
    genetic divergence caused by natural selection for different habitats or resources; apple and hawthorn maggot flies

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