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Traits are expressed at an..
Individual level
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Evolution happens at a...
Population level
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Evolution
Change in the allele frequency of a population over time
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Natural populations
are always evolving, which means that allele frequencies in their gene pool are always changing over generations.
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Mutation is the source of new alleles
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GE: #2
The population is infinitely large
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GE: #3
The population is isolated from all other populations of the species (no gene flow)
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GE: #5
All individuals survive and produce the same number of offspring
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Evolution is an opportunistic process.
Dramatic shifts have a tendency to occur to smaller populations rather than larger ones.
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Violation of GE 5
- Natural selection
- a. Directional selection: one extreme or other extreme of parabola : environment favored selection
- b. Stabilizing selection: Middle of parabola. extreme forms become lessened
- c. Disruptive selection: both sides of parabola: extreme forms favored by environment.
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Violation of GE 4
- Sexual selection; individuals with more attractive traits, better being able to attract mates for off spring generating.
- ex. peacock tails
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Violation of GE 2
- Genetic Drift: Stochastic fluctuation in allele frequency of a population over time.
- Stochastic= Random
- ex. Bottle neck effect: drastic reduction in population size, brought about by SEVERE PRESSURE or a random event.
- aka. selective pressure
- some alleles are no longer going to be present.
- Founder effect- migration of alleles vs. dying off
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Violation of GE 3
gene glow: movement of alleles among population
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Pre-zygotic isolation mechanism, how many?
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1- Temporal Isolation
- 2- Mechanical Isolation
- 3- Behavioral Isolation
- 4- Ecological Isolation
- 5- Gametic incompatibility
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Temporal isolation
Indv. of diff populations can evolve and reproduce at diff times
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mechanical isolation
instability to reproduce because of physical incapability
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behavioral isolation
ind. of one pop. may not be attracted to an indv. of another pop
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ecological isolation
indv. are in diff places and do not meet
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gametic incompatibility
reproduction cells meet up but do not fertilize
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Post Zygotic Isolation
- 1- Hybrid Inviability
- 2- Hybrid Sterility
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speciation
process by which idv. diverge into separate liniages and become diff species
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hybrid inviability
hybrid, idv. die before they can reproduce
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hybrid sterility
hybrid ind. unable to produce offspring, unfunctional gametes
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sympatric
no physical separation between populations
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allopatric
physical separation between species
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Biological Species concept
species are groups of interbreeding natural populations that are REPRODUCTIVELY ISOLATED FROM OTHER SUCH GROUPS.
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