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speciation - Speciation Chapters 17 and 18 Speciation...

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Speciation Chapters 17 and 18. Speciation: splitting of one species into 2 different species. What is a species? Based on ability to reproduce. “Biological species concept”: a species is a group of organisms that interbreed under natural conditions and that are reproductively isolated from each other. Reproductively isolated: don’t produce fertile hybrids. Natural conditions: artificial breeding doesn’t count. For example, artificial insemination, keeping 2 species locked up together. In contrast, the older “morphological species concept”: members of the same species look similar to each other. Many examples of organisms that look similar but can’t produce fertile offspring. Problems with biological species concept: Doesn’t work with fossils or extinct species. Doesn’t work with asexual species , such as most bacteria. How to deal with what is “natural”.
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Reproductive Isolation How do populations become reproductively isolated? Result of gene mutations and altered allele frequencies due to selection and genetic drift. To maintain as a single species, there must be gene flow between populations: matings between members of separated populations that allow mixing of alleles. In the absence of gene flow, mutations in different populations will be independent, and allele frequencies will change independently of each other. In most cases, migration is the key to gene flow. Once gene flow stops: genetic divergence occurs. The two populations gradually become genetically different. Speciation sometimes occurs very quickly, other times more slowly. In most cases it is not an instantaneous event.
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Genetic Divergence
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Reproductive Isolation Mechanisms Pre-zygotic (before mating) vs. post- zygotic (after mating).
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