BIOLOGY 202L Lecture Notes - Lecture 17: Molecular Clock, Genetic Drift, Chromosome
21 Jan 2016
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Document Summary
Two separate species if reproductively isolated from each other where they co-occur. Either pre-zygotic or post-zygotic: pre-zygotic: prevents hybrids from being formed whatsoever, post-zygotic: reduced hybrid viability; hybrid sterility. If two species create viable f1 offspring but the f1"s do not form f2"s, then essentially sterile f1s. Extrinsic/ecological isolation in nature, cannot exist in parental habitat. Evolution of prezygotic barriers (increased mate discrimination) would decrease the f1s created. Causes natural selection to prevent matings among the species. Direct fitness advantage to carefully choosing one"s mate(s) for rare traits, we expect rare alleles (causal) and common alleles strong purifying selection for intermediate traits, we expect a balance between causal and. Take-aways from the two speakers look at ppts. Schmitt: origin of humans from apes, traits distinguishing humans from primates, possible reasons for bipedal evolution, transitional forms: mixtures of old and new traits, all of these fossils have mixture of primitive/ancestral and. Close relative lecture advanced/derived traits (old and new)
