2.Species_and_Speciation-2[1]

2.Species_and_Speciation-2[1] - • In sympatric speciation...

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Unformatted text preview: • In sympatric speciation , new species arise within the range of the parent populations. – Here reproductive barriers must evolve between sympatric populations – In plants, sympatric speciation can result from accidents during cell division that result in extra sets of chromosomes, a mutant condition known as polyploidy . – In animals, it may result from gene-based shifts in habitat or mate preference. 2. Sympatric speciation: a new species can originate in the geographic midst of the parent species • An individual can have more that two sets of chromosomes from a single species if a failure in meiosis results in a tetraploid (4n) individual. • This autopolyploid mutant can reproduce with itself (self-pollination) or with other tetraploids. It cannot mate with diploids from the original population. • Autopolyploidy : where one species doubles its chromo- some number and forms a potentially new species. Fig. 24.10 • In the early 1900s, botanist Hugo de Vries produced a new primrose species, the tetraploid Oenotheria gigas , from the diploid Oenothera lamarckiana . – This plant could not interbreed with the diploid species. • Another mechanism of producing polyploid individuals occurs when individuals are produced by the matings of two different species, an allopolyploid . – While the hybrids are usually sterile, they may be quite vigorous and propagate asexually. – Various mechanisms can transform a sterile hybrid into a fertile polyploid. – These polyploid hybrids are fertile with each other but cannot interbreed with either parent species. • One mechanism for allopolyploid speciation in plants involves several cross-pollination events between two species or their offspring, and perhaps a failure of meiotic disjunction to a viable fertile hybrid whose chromosome number is the sum of the chromosomes in the two parent species. Fig. 24.11 Note: Nearly 100,000 species of plants are allopolyploids! • Many plants important for agriculture are the products of polyploidy. – For example, oats, cotton, potatoes, tobacco, and wheat are polyploid. – Plant geneticists now hydridize plants and use chemicals that induce meiotic and mitotic errors to create new polyploids with special qualities. • Sympatric speciation is one mechanism that has been proposed for the explosive adaptive radiation of almost 200 species of cichlid Fshes in Lake Victoria, Africa. – While these species clearly are specialized for exploiting different food resources and other resources, non-random mating in which females select males based on a certain appearance has probably contributed too. • Traditional evolutionary trees diagram the diversifcation oF species as a gradual divergence over long spans oF time....
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This note was uploaded on 09/23/2011 for the course BIOL 240 taught by Professor Staff during the Spring '11 term at S.F. State.

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2.Species_and_Speciation-2[1] - • In sympatric speciation...

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