Evolution part 1

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Evolution part 1
2010-01-18 00:06:27
Bio Midterm

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  1. taxonomy
    Ordered division of organisms into categories based on a set of characteristics used to assess similarities and differences, leading to a classification scheme; the branch of biology concerned with naming and classifying the diverse forms of life.
  2. sedimentary rock
    • Rock formed from sand and mud that once settled in layers on the bottom of seas, lakes, and marshes.
    • Sedimentary rocks are often rich in fossils.
  3. catastrophism
    The hypothesis by Georges Cuvier that each boundary between strata corresponded in time to a catastrophe, such as a flood or drought, that had destroyed many of the species living there at that time.
  4. gradualism
    A view of Earth’s history that attributes profound change to the cumulative product of slow but continuous processes.
  5. uniformitarianism
    Charles Lyell’s idea that geologic processes have not changed throughout Earth’s history.
  6. descent with modification
    Darwin’s initial phrase for the general process of evolution.
  7. artificial selection
    • The selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits.
    • As a result of artificial selection, crop plants and animals bred as livestock or pets often bear little resemblance to their wild ancestors
  8. homology
    Similarity in characteristics resulting from a shared ancestry.
  9. homologous structures
    • Structures in different species that are similar because of common ancestry.
    • The arms, forelegs, flippers, and wings of different mammals are homologous structures
  10. vestigialorgans
    • A structure of marginal, if any, importance to an organism. Vestigial organs are historical remnants of structures that had important functions in ancestors.
    • These are a type of homologous structure.
  11. biogeography
    • The study of the past and present distribution of species.
    • Closely related species tend to be found in the same geographic region, whereas the same ecological niches in distant regions are occupied by very different (though sometimes similar-looking) species.
  12. endemic species
    Species that are confined to a specific, relatively small geographic area.
  13. microevolution
    Evolutionary change below the species level; change in the genetic makeup of a population from generation to generation.
  14. modern synthesis
    A comprehensive theory of evolution emphasizing populations as units of evolution and integrating ideas from many fields, including genetics, statistics, paleontology, taxonomy, and biogeography.
  15. population
    • A localized group of individuals that belong to the same biological species (that are capable of interbreeding and producing fertile offspring).
    • Populations of the same species may be isolated from one another, thus exchanging genetic material only rarely. Such isolation is common for populations confined to different, widely separated islands or lakes.
  16. gene pool
    • The total aggregate of genes in a population at any one time.
    • If only one allele exists at a particular locus in a population, that allele is said to be fixed in the gene pool, and all individuals are homozygous for that allele.
  17. Hardy-Weinberg theorem
    The principle that frequencies of alleles and genotypes in a population remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work.
  18. Hardy-Weinberg equilibrium
    • The condition describing a non-evolving population (one that is in genetic equilibrium).
    • p2 + 2pq + q2 = 1
    • 1. Extremely large population size. The smaller the population, the greater the role played by chance fluctuations in allele frequencies from one generation to the next, known as genetic drift.
    • 2.No gene flow. Gene flow, the transfer of alleles between populations, can alter allele frequencies.
    • 3.No mutations. By introducing or removing genes from chromosomes or by changing one allele into another, mutations modify the gene pool.
    • 4.Random mating. If individuals preferentially choose mates with certain genotypes, including close relatives (inbreeding), random mixing of gametes does not occur.
    • 5.No natural selection. Differential survival and reproductive success of individuals carrying different genotypes will alter allele frequencies.
  19. duplication
    A mutation in chromosome structure due to fusion with a fragment from a homologous chromosome, such that a portion of a chromosome is duplicated.
  20. genetic drift
    • Unpredictable fluctuations in allele frequencies from one generation to the next because of a population’s finite size.
    • Two situations that can increase the likelihood that genetic drift will have a large impact on a population are referred to as the bottleneck effect and the founder effect.
  21. bottleneck effect
    • Genetic drift resulting from the reduction of a population, typically by a natural disaster, such that the surviving population is no longer genetically representative of the original population.
    • By chance, certain alleles may be overrepresented among the survivors, others may be underrepresented, and some may be eliminated altogether. Genetic drift may continue to substantially change the gene pool for many generations until the population is large enough that chance fluctuations have less effect.
  22. founder effect
    • Genetic drift that occurs when a few individuals become isolated from a larger population, with the result that the new population’s gene pool is not reflective of the original population.
    • Can occur when a few members of a population colonize a new location. These founders pass through an “isolation bottleneck” and represent a distinct gene pool with different allele frequencies from those of the parent population.
  23. gene flow
    • Genetic additions to or substractions from a population resulting from the movement of fertile individuals or gametes.
    • Gene flow tends to reduce differences between populations
  24. phenotypic polymorphism
    The existence of two or more distinct morphs (discrete forms), each represented in a population in high enough frequencies to be readily noticeable.
  25. genetic polymorphism
    • The existence of two or more distinct alleles at a given locus in a population’s gene pool.
    • The heritable component of height is the result of such genetic polymorphisms for alleles at the several loci that influence height.
  26. average heterozygosity
    The percent, on average, of a population’s loci that are heterozygous in members of the population
  27. cline
    • A graded variation in a trait that parallels a gradient in the environment.
    • For example, the average body size of many North American species of birds and mammals increases gradually with increasing latitude. Presumably, the reduced ratio of surface area to volume that accompanies larger size is an adaptation that helps animals conserve body heat in cold environments.
  28. fitness
    The contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals.
  29. relative fitness
    The contribution of one genotype to the next generation compared to that of alternative genotypes for the same locus.
  30. directional selection
    • Natural selection that favors individuals at one end of the phenotypic range.
    • Shifts the frequency curve for some phenotypic character in one direction or the other by favoring individuals that deviate from the average.
  31. disruptive selection
    • Natural selection that favors individuals on both extremes of a phenotypic range over intermediate phenotypes.
    • Can be important in the early stages of speciation.
  32. stabilizing selection
    • Natural selection that favors intermediate variants by acting against extreme phenotypes.
    • This mode of selection reduces variation and maintains the status quo for a particular phenotypic character.
  33. balancing selection
    Natural selection that maintains stable frequencies of two or more phenotypic forms in a population (balanced polymorphism).
  34. balanced polymorphism
    The ability of natural selection to maintain diversity in a population.
  35. heterozygote advantage
    Greater reproductive success of heterozygous individuals compared to homozygotes; tends to preserve variation in gene pools.
  36. frequency-dependent selection
    A decline in the reproductive success of a morph resulting from the morph’s phenotype becoming too common in a population; a cause of balanced polymorphism in populations.
  37. neutral variation
    Genetic diversity that confers no apparent selective advantage.
  38. pseudogene
    A DNA segment very similar to a real gene but which does not yield a functional product; a gene that has become inactivated in a particular species because of mutation.
  39. sexual dimorphism
    • A special case of polymorphism based on the distinction between the secondary sex characteristics of males and females.
    • These distinctions include differences in size, color, and ornamentation. In vertebrates, males are usually the showier sex.
  40. intrasexual selection
    A direct competition among individuals of one sex (usually the males in vertebrates) for mates of the opposite sex.
  41. intersexual selection
    Selection whereby individuals of one sex (usually females) are choosy in selecting their mates from individuals of the other sex; also called mate choice.
  42. What are the constraints on evolution?
    • 1. Evolution is limited by historical constraints. Evolution does not scrap ancestral anatomy and build each new complex structure from scratch; it co-opts existing structures and adapts them to new situations.
    • 2. Adaptations are often compromises. A seal spends part of its time on rocks; it could probably walk better if it had legs instead of flippers, but it would not swim nearly as well
    • 3. Chance and natural selection interact.
    • 4. Selection can only edit existing variations.