Evolution (EEMB 131)

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Evolution (EEMB 131)
2012-02-14 12:14:01
131 Evo

Midterm 1
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  1. Early Concepts of the Diversity in Nature ( overview )
    • Stasis ( cyclical stasis)
    • Book of Genesis
    • Imperfect --> perfect
    • Harmony
  2. Lamark
    • Scala Naturae : primitive organisms were continually being made. These would then progress into more complex/ more perfect organisms
    • ex. Fish --> repitles--> mammals --> angels
    • Independent creations which evolutionary progressed into more advanced t ypes
    • First idea about evolutionary mobility to counteract the static idea
  3. Cuiver
    • Wanted to dispell lamark's idea and replace it with a static theory
    • Said that organisms were already perfectly adapted to their environment
    • Faunal sucesscion is not from adapation, but to mass extinctions followed by the creation of new fauna
  4. Natural Theology
    • Had elements of Cuvier's idea that thigns were perfectly adapted to their environments
    • World as a machine with parts that fit perfectly so that there was no place for competition or adaptations
    • Variations were levels of imperfection ( therefore selection could only weed out)
  5. Malthus
    • Said that the economy of nature was harsh and in a competitive disequilibrium
    • People grew at an exponential rate while resources could not be replenished at the same rate
    • Wars, famine, etc
  6. Pre-Mendelian Genetics
    • Thought heritable features were blended
    • ( like cans of paint)
    • Blending made the idea of rare traits persisting to be impossible because the trait would only be diluted with each generation
  7. Early Geneticists
    • Used experiments with visual mutations
    • these were often Rare on a per loci/ per generation basis
    • Often they were also deleterious
    • Thought most individuals were homozygous for w/t
  8. How did early theories of evolution make Darwin's theory of selection impossibe
    • Early genetic thinking of "blending"
    • Natural Theology: idea of static harmonious organisms, No struggle for existance
    • Variations of imperfection vs Perfect ( no possibility of more perfect"
  9. Microgeographic variation
    • scale : within populations
    • speciation potential : v. Low
    • GSE>GF>Selection
    • Bc of GSE influence.. proceeds in a random and chaotic manner
  10. Macrogeographic
    • -encompases a larger area that increases the size of the population and chance of environmental heterogeneity
    • Inc Enviro. heterogeneity translates into differences in fitness with selection against low fitness.
    • -GSE is diminished bc it exponentially decreases at population size increases

    scale: within populations
  11. Eco Geographic
    • Scale: among species affects unrelated species
    • ability to respond is genetic but the response is non genetic
    • Allen's rule, Groger's rule, Bergmann's rule
  12. Basic allopatric step cline
    • Difference between parapatric cline: is that allopatric cline was created in the abscence of GF.
    • A step cline would be created when 2 seperate populations meet and there was no prior adaptation to different environmental pressures. These two populations would interbreed and create hybrids creating a crisis. If these hybrids face a fitness penalty then assortive mating will be an advantage and the cline will not broaden. However, if no fitness penalty for the hybrids, gene flow will be able to erase the differences between the populations.
  13. Basic Parapatric step cline
    • selection can create and maintain a steep cline across a steep environmental gradient
    • Selection continually steepens the step cline due to there being a different "most fit" genotype along the cline.
    • Selection is counteracting the effects of the GF homogenizing the populations.
  14. Stable and Unpredictable environment
  15. Unstable and Predictable
    Favors adaptations that reduce death rate in a declining population. "slow dying" like hibernation in a seasonal environment.
  16. Definition of Species
    Genetic : Reproductively isolated ( via chromosomal rearrangment that produce individuals that are incompatible with their parents and siblings. THere is a built in qualification that these individals must be success to be a new species. however, this qualification is artifical. Successful establishment increases as the founding number of individuals increases.
  17. Successful establisment
    The ability that a new reproductively isolated individual can 'successfully' become established as a new species.
  18. Generation of Variation
    • arise through both
    • Recombination ( of exisiting alleles)
    • Mutations ( process that crates new alleles)
  19. How do mutations form
    • transitions, mispairing, failure of DNA repair mechanism base subsititution, base or segment insertion/deletion
    • Chromosomal structural alteration deletions, transversion, duplication

    Rare that mutation will be benificial and convey some advantage

    Neutral and nearly neutral genes can acculmulate in a population by genetic sampling error over time
  20. How do mutations become alleles
    Through the enormous summation of individuals in a population that carry this mutation over many generations
  21. What role does recombination play in genetic variation
    within a population in a given time, recombination is the process which is responible for the genetic variation. Recombination breaks up chromosomes so that the alleles can sort independently and produce many many different combinations of genes in gametogenesis. This creates a large range of diversity alone, and the fusion of two gametes further increases the diversity.
  22. Classical school of population genetic theory
    • In a population there is very little variability causes by mutation
    • Most individuals are homozygous for w/t, and rarely was there heterzygous for some mutation
    • Mutations were rare
    • Variation was higher inbetween populations than w/in populations
    • Selection was weeding
    • Genetic outlook was mostly static
  23. Balance school of genetic theory
    • Genetic diversity at one time is largely due to recombination shuffling the exisiting alleles into new combinations
    • Variation w/in population was not much less than variation within populations

    • Selection is against the less fit but can result in individuals what are "more perfect"
    • speciation modes were ongoing
    • heterozygousity was common
  24. Why is HW usefull
    • A. often the allelic frequencies are sampled and not fully enumerated so that this creates a margin of error that masks small violations
    • B. the violations of HW are the mechanisms of evolutionary change
  25. HW is the yardstick of ____(micro or macro ) evolution
    Micro ( genes) within a population
  26. The "memory" of HW
    • HW does NOT have a memory
    • Depending on the parental allelic frequency, recombination should allocate the alleles in the next generation in some sort of equilibrium.

    If there are some violations, then the new generation will have a new equilibrium state, but if there are none the equilibrium values will not change
  27. Factors that affect HW
    • Directional ( affects few loci)
    • 1. non random mating
    • 2. selection
    • 3. possibly GF

    • Random ( affects many loci)
    • 1. GSE
    • 2. poss GF
    • 3. Population size
  28. GSE
    • 1. predominately is Genetic Drift
    • ( not enough individuals to represent ALL combinations of alleles )

    • Strong effect in small populations
    • Decreases effect exponentially as population size increaes
    • Often results in loss of alleles
    • Can be countered with Gene Flow

    ex. Founder effect, bottle-necking
  29. Gene Flow vs GSE
    • Gene flow can potentially restore lost alleles by ( GSE)
    • Gene flow can retard differences generated by selection

    Endler's Model

    patch size was dependent on GSE and GF, with increases GF the patch would equiliberate at a larger patch size
  30. Selection and Fitness
    • =1-w
    • is measured in RELATIVE terms associated with a particular allele or genotype
    • Overall fitness is difficult ot measure since it is a statement about the FUTURE
    • Fitness depends on the environment and genetic composition

    • Selection can act on individual alleles over a time span
    • Selection can occur at anytime prior to cessation of reprodcuction ( so gametes, larva, seeds are succeptible)
  31. If to the right of the graph of population size does Selection always win against GF
    Because it is consistantly directional, even if slow or small, will be directional whereas geneflow is Random
  32. Why does GSE dominate to the left of the graph of increasing population size
    • GSE Pre-empts selection and geneflow by happening during meiosis at at fertilization
    • GF and Selection usually affects Diploid individuals
  33. Selection
    • Acts on individuals
    • but can act on alleles over timespan
    • Can occur at anytime prior to cessation of reproduction
    • is the consequence of differential fitness
  34. Adaptation
    • How individuals cope with differential environmental factors through modification of behavior, physiology, or morphology
    • adaptation is the result of selection
    • Adaptations can not be deleterious
    • Can be measured in Absolute terms ( many indidviduals can have the same value)
    • Adaptations of a species is the summed results of selection on a individual level
  35. Types of adaptatoin varies with fitness
    • ^ fitness , ^ adapation ( normally)
    • ^fitness, v adapatation ( fertilization advantage/ sexual selection)
    • v fitness, ^ adaptation ( can not happen unless by GSE)
    • v fitness, v adapation ( not possible)
    • - why?
  36. adaptive strategies
    • R: unpredictable, unstable
    • K:predictable, Stable
    • Anti -z : Predictable , unstable

    Unpredictable, stable ( is NOT possible)