Natural selection

Card Set Information

Author:
doncheto
ID:
307812
Filename:
Natural selection
Updated:
2015-09-14 14:42:13
Tags:
naturalselection natural selection genetics
Folders:

Description:
pop marine gen
Show Answers:

Home > Flashcards > Print Preview

The flashcards below were created by user doncheto on FreezingBlue Flashcards. What would you like to do?


  1. Theory of Natural Selection
    • • Three conditions for Natural Selection:
    • 1) Variation in traits
    • 2) Heritability
    • 3) Overproduction of offspring
    • 4) Survival and reproduction is not random
    • • Natural selection ≠ “Survival of the fitest”
  2. Variation and Heritability
    • • Observations from Lamarck and Erasmus Darwin
    • that offspring are not exactly like parents (change
    • can occur in a single generation)
    • • Observed the commonly known facts that:
    • – all individuals are not alike (i.e., there are different
    • phenotypes)
    • – Offspring inherit the majority of their traits from their
    • parents.
  3. Variation can be:
    • CONTINUOUS: having a
    • multitude of variants (e.g.,
    • colour bands in the snail)


    • DISCRETE: limited # of types
    • (such as blood types)
  4. Heritability in Diploids
    • Two copies of each gene (diploid)
    • – Humans have 23 chromosomes, 2 copies of each,
    • for a total of 46 chromosomes)
    • Each egg or sperm has only one copy of each
    • chromosome
  5. Passing on genes is like tossing coins
    • • Two copies exist for each gene
    • • Whether you pass on a certain
    • copy of a gene is an
    • independent event for each
    • child
    • • If you have two children,
    • sometimes you will pass on the
    • same copy to both children
    • (leaving the second copy passed
    • on to neither child)
  6. Competition
    • • More offspring are produced than there are
    • resources to support
    • • Creates a “struggle for existence”
    • • Some offspring will be better at surviving and
    • reproducing than others (i.e., have higher fitness)
  7. Fitness
    • – the number of offspring an individual produces
    • that survive to reproduce themselves
    • • Fitness = 1.0 means that individuals of this
    • phenotype are successfully passing on 100%
    • of their genes, on average
    • • Fitness = the number of genes passed on to the next genera)on • Because diploid organisms (i.e., most organisms) only pass on half of their genes to each child, they must have two offspring living to reproductive age to have Fitness = 1
    • • Fitness = 1 does not exactly mean that you have passed on 100% of your genes to the next generation (Remember: sometimes you send two copies of the same gene and zero copies of the other)
  8. Outcome
    • • Some phenotypes will be better represented in the
    • next generation than they are in the present
    • generation
    • • Could be extended: some entire lineages may be
    • more successful than others as well resulting in some
    • lineages going extinct (as Cuvier had found)
  9. Natural selection will not take place if:
    • • there is no variation – E.g., No humans have gills, so we cannot select for them,
    • regardless of how beneficial they might be
    • • If the gene is not heritable – E.g., Working out and gehng a strong heart might make
    • you live longer and have more children but selection can
    • not act upon it if is not a genetic trait
    • • If there is no difference in survivorship or
    • reproductive ability between variants – E.g., Having attached or free earlobes doesn’t really matter
  10. “Survival of the fittest”
    • • This saying is a bit misleading and doesn’t
    • quite capture the essence of what is natural
    • selection
    • • You can be as “fit” an individual as can be but
    • it is the ability to reproduce that is the key
    • feature for an increase in representation in the
    • next generation
  11. Characteristics of Natural Selection
    • – dependent on the variation present in the
    • population
    • – Short-sighted – acts only present selection
    • pressures
  12. Sources of variation
    • • Gene flow: immigration
    • • recombination
    • • ultimately, from mutation
  13. Mutation at the Phenotype Level
    • • Mutations can be:
    • – beneficial
    • – detrimental
    • – neutral
  14. Mutation at the DNA Level
    • • A mutation is caused
    • when the
    • chromosomal
    • machinery makes a
    • mistake
    • (Know types of mutations)
  15. Mutagens
    • – radiation
    • – certain chemicals (e.g.
    • carcinogens)
  16. Variation is random
    • • When a new recombinant or mutant genotype
    • arises, there is no tendency for it to arise in
    • the direction of improved adaptation
    • • Natural selection imposes direction on
    • evolution, using undirected variation
  17. Scale of Natural Selection
    • • Natural selection happens at the scale of an
    • individual
    • • Evolution happens at the scale of a population
  18. Types of Natural Selection
    • • Three kinds of natural selection:
    • – Directional selection
    • – Stabilizing selection
    • – Disruptive selection
  19. Directional Selection
    • Larger individuals may have higher fitness
    • (i.e., produce more offspring) than smaller
    • individuals.
    • Fishing industry
    • produces selection
    • that favours smaller
    • cod and can
    • produce a decrease
    • in average body
    • size.
  20. Stabilizing selection
    • The average members of the population may
    • have higher fitness than the extremes.
    • Babies of intermediate
    • birth weight have higher
    • survivorship than very
    • small and very large
    • babies
  21. Disruptive selection
    • Natural selection could favour both extremes
    • over the intermediate types

    • In the finch,
    • Pyrenestes
    • ostrinus
    • both very large
    • and very small
    • bills are beneficial
    • for eating large
    • and small
    • seeds, respectively
  22. • Examples of natural selection
    • • beak size has a lot to
    • do with how well a
    • finch feeds on certain
    • seeds
    • • seeds of Tribulus have
    • the toughest seed
    • coat that requires a
    • large beak to break
    • Drought causes collapse of food supply,
    • survival plummets
    • High mortality in smaller individuals,
    • strong selec)on for large birds that can
    • crack large, tough seeds
  23. Human-induced selection
    • 1) Natural pop’n with
    • variation for insecticide
    • resistance
    • 2) Insec)cide appl’n kills
    • all but those with
    • resistance
    • 3) Surviving insects breed
    • new generation of
    • insecticide resistance
    • population
  24. Summary
    • • Natural Selection acts on whatever variation is
    • present at the time. This variation is generated
    • randomly with respect to selection pressures
    • • Selection can be directional, stabilizing or disruptive
    • • Random factors can also play a part in evolution

What would you like to do?

Home > Flashcards > Print Preview