-
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
-
Genic --> due to genetic DRIFT
- single gene causes this
- Mechanical Isolation: ie b/w dextral & sinistral coiling varieties of snail Euhadra aomeriensis
- CLADOgenesis
-
Chromosomal - autopolyploidy
- autopolyploidy: chromosome sets derived from 1 ancestral species
- F1 hybrid inviability: ie tetraploid clawed toads & diploid
- anagenesis or CLADOgenesis
-
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
-
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)
-
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.
-
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)
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