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19 Cards in this Set
- Front
- Back
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Speciation |
Formation of new species, as populations become reproductively isolated and no gene flow occurs |
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Allopatric Speciation |
Occurs through geographical isolation Physically isolates a population, accumulate genetic differences, no longer can reproduce successfully eventually |
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Sympatric Speciation |
Occurs without geographical isolation Usually disruptive selection in animals and ploidy in plants |
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Vicariance |
Large scale allopatric speciation through large scale geophysical events Eg. Breakoff of islands from Gondwana |
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What are reproductive isolating mechanisms |
Any factor that acts to prevent interpreting between two species Barrier to gene flow |
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2 main RIM |
Prezygotic (prior to mating or fertilization) Postzygotic (acts after fertilization) |
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List of Prezygotic RIM |
Geographical-Physical barrier,melting of ice broke NZ into two kaka speciated Ecological isolation-Same geographical isolation but occupy different niches,eat different host plants Temporal isolation-Mating at different prices nonoverlapping times, silver and red pine shed pollen at different times Behavioral isolation-Differences in behaviour usually concerning mating and rituals, cricket song makes mates unrecognizable Structural barriers-Reproductive organs are incompatible, damselfly praises Gamete incompatibility-Sperm cannot fertilize egg of different species, incorrect chemoreceptors, cannot penetrate surface |
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Gene Flow |
The movement of alleles between two populations of the same species and occurs when individuals migrate between original population and breed with a resident in destination population |
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List of Postzygotic RIM |
Hybrid inviability - embryo, zygote or offspring dies early in development Hybrid sterility - maturity reached but cannot breed Hybrid breakdown - can breed but subsequent generations infertile |
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Genetic Drift |
The random change in allele frequency in the gene pool, instead of selection. Significant in small populations as higher probability of alleles being fixed or lost |
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Founder Effect |
When a small population becomes isolated from the main, so allele frequency not representative of original and more subject to genetic drift Limited genetic drift, inbreeding etc |
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Bottleneck Effect |
When a large population is suddenly reduced in size Human or natural. Random alteration of allele frequency so no longer representative. Subject to drift when in bottleneck phase |
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Population |
Members of a species that live in the same geographical location and have a common gene pool |
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Deme |
A local population with limited gene flow to a larger population. Local selection pressures mean phenotypes of different demes are different |
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Cline |
Pattern of variation between individuals with a continuous inc or dec of phenotypic characteristics between adjacent populations Ends could be different enough for speciation |
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Ring Species |
Cline formed a circle (often around globe) where ends meet and diff species formed. Range of intermediate species |
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Extinction |
Numbers less than critical level, birth rate too low, leaves vacant niche Often in rapid environmental change Specialists vs generalists different likelihood of survival Lack of genetic diversify increases chance of extinction |
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Natural Selection |
Process by which inheritance traits that make an individual more likely to survive long enough in environment to reproduce and become more common |
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Types of Selection Pressures (4) |
Stabilising - Extreme phenotypes selected against Disruptive - Extreme phenotypes selected for, average selected against Directional - One extreme selected for or against, allele frequency shifts continuously in one direction Sexual - Heritable characteristics of winning males passed on |
