BIOL 1102 Lecture Notes - Lecture 27: Parapatric Speciation, Outbreeding Depression, Allopatric Speciation

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12:14 pm: macro-evolution: evolution above the level of populations (species and above). Inbreeding depression >>> normal fitness >>> heterosis >> (same species) > outbreeding depression >> (speciation occurs in here somewhere) > reproductive isolation (different species) Inbreeding depression: decreased fitness breeding individuals too closely related. Offspring homozygous at many genes: heterosis, hybrid vigor. Mutts healthier than purebreds: outbreeding depression, decreased fitness breeding individuals too genetically different. Epistasis and pleiotropy cause poor gene interactions: reproductive isolation, no gene flow. For example, wheat and rye are often hybridized to form triticale, which has desirable traits of both parent species, but the first hybrids are sterile. Researchers then use colchicine chemicals to black microtubule formation during cell division. This causes non- disjunction and polyploidy in the gametes. Then you can mat two polypoid hybrids together successfully. Polypoid plants may have better fitness than monoploids: extinction, facts about extinction, fossil records show at least 20 large scale extinction events.

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