rates of speciation and mechanisms T. 30 final exam.txt

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rates of speciation and mechanisms T. 30 final exam.txt
2011-12-11 12:43:58
rate speciation mechanisms

evol bio
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  1. Genic --> due to selection
    • change of one locus or few loci
    • Due to
    • 1. F1 hybrid inviability @ one locus: ie copper tolerance in Mimulus guttatus. Selective forces are METALS
    • 2. F2 hybrid breakdown @ 2 loci: ie Indian rice crossed w/Japanese rice, both same species but different varieties
    • CLADOgenesis
  2. Genic --> due to genetic DRIFT
    • single gene causes this
    • Mechanical Isolation: ie b/w dextral & sinistral coiling varieties of snail Euhadra aomeriensis
    • CLADOgenesis
  3. Chromosomal - autopolyploidy
    • autopolyploidy: chromosome sets derived from 1 ancestral species
    • F1 hybrid inviability: ie tetraploid clawed toads & diploid
    • anagenesis or CLADOgenesis
  4. Chromosomal - allopolyploidy
    • allopolyploidy: polyploids w/chromosomes derived from different species
    • Due to MUTATION & Maintained by natural SELECTION
    • F1 Hybrid Sterility: b/w tobacco plant Nicotiniarat abacum (2n=48) CROSS w/ N. glutinosa (2n=24) = sterile hybrid (2n=36).
    • This retains fertility AFTER doubling event where 2n=72…produces N. digluta
  5. Chromosomal - recombinational
    • Due to MUTATION & Maintained by natural SELECTION
    • Ecological F1 inferiority: ie, ISOLATES desert sunflower Helianthus anomalus (2n=34) from its parental grassland species H amnus (2n=34) and H petiolaris (2n=34)
  6. Genic…..due to disruptive selection
    • SLOW mechanism
    • Accounts for Drosophila speciation
    • multiple reinforcement of post-zygotic & pre-zygotic isolation b/w Drosophila melanogaster & D. simulans over ~5mil years.
  7. Genic…..due to stabilizing selection
    • SLOW mechanism
    • Stabilizing selection OPPOSES speciation
    • NO hybrid sterility: ie western sycamore trees (Platanus occidentalis) & eastern sycamore trees (P. orientalis), as evident by F1 HYBRID London plane tree (P. hybrida), in spite of over 30mil years of geographic isolation due to vicariance (barrier = Ocean)