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11-28-11 Species & Speciation II - How do species arise

11-28-11 Species & Speciation II - How do species...

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ZOL445 Evolution November 28, 2011 Species & Speciation II: How do new species arise? How do new species arise? 1. Genetic isolation 2. Divergence 3. Reproductive isolation Traditionally, these steps were thought to occur in sequence, but there is evidence that isolation and divergence can occur at the same time and place. Further, in many cases, there may not be subsequent reproductive isolation Types of speciation: Allopatric : Barrier is formed, and two populations diverge in isolation Peripatric : Small fraction of the original population enters a new niche, the two populations diverge in isolation. Parapatric : Fraction of original population enters new niche, two populations diverge in adjacent niches. Sympatric : Two phenotypes clearly exist and diverge within the population.
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Unformatted text preview: Genetic Isolation Physical barriers can inhibit gene flow and lead to speciation Physical isolation through dispersal (Hawaii islands) Physical isolation through vicariance (actual physical barrier) Genetic isolation through polyploidy o Polyploids can arise through failure to complete meiosis o Tetraploids can only mate with tetraploids (mate selectivity) Tetraploids are typically sterile because homologous chromosomes do not pair correctly during meiosis Genetic isolation through chromosomal inversion o The offspring will be selected against, leading to a loss of one chromosome or reproductive isolation between the homozygotes...
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