Ch.18 - 18.2 o Species are the fundamental taxonomic units...

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18.2 o Species are the fundamental taxonomic units of biological classification Biological Species Concept (BSC) s Group of organisms that can successfully interbreed and produce viable fertile offspring s Defines species in terms of population genetics and evolutionary theory in static world s Alludes (refers) to the genetic cohesiveness (close-sticking together) of species s Can explain why organism look alike s If phenotypes reflect genotype, members of the same gene pool should share genetic traits (genotype) that determine phenotype s Population of same species are said to experience gene flow that mixes their genetic material and could be the “glue” holding a species together s However in order for speciation to occur, it is essential that species are reproductively isolated (gene flow-inbreeding [mating with relatives] must stop) otherwise no new specie forms Morphological Species Concept (MSC) s Visible morphological traits s Paleontologists use morphology to identify fossils Phylogenetic Species Concept (PSC) s Group of organisms bound by a unique ancestry Ecological Species Concept (ESC) s Group of organism that share a distinct ecological niche s Niche: a position particularly well suited to the person who occupies it For advantages and disadvantages of the following species definitions, refer to the Prof PDF Hybridization: s When two species interbreed and produce fertile offspring s Hybridization between species produces sterile offspring as well s Sterile hybrids results when horses mate with zebras or horses vs. donkeys, or lions vs. tigers s Female Donkey vs. male horse produces mules s According to BSC, hybrids don’t exist s Recombination is a principal advantage of sexual reproduction s However, asexually reproducing populations have higher frequency of mutation while sexually reproducing have higher recombination rate s Hybridization can be an effective way of achieving major and rapid evolution
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18.6 Ring Species : Genes flowing between some populations s Adjacent populations of these so-called ring species can exchange genetic material directly (ex salamander on slides) s However, gene flow between distant populations occurs only through intermediary (link) populations s In the case of salamanders, seven subspecies differ in traits, colour, size and ecology s Adjacent subspecies of salamander often interbreed, therefore, their intermediate phenotype is common s In other parts, where the ring is not closed , the two subspecies rarely interbreed as they appear to have differentiated to an extent that they can no longer exchange genetic material s So are these two groups’ subspecies or different species? s Since they still have potential to exchange genetic material through the “ intervening population ”, that form the ring, we can say they belong to the same species s Most likely the southern subspecies represent an intermediate stage of new species formation Clinal Variation: change along a Gradient s Pattern of smooth variation along the geographic gradient
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This note was uploaded on 04/02/2011 for the course BIO 1010 taught by Professor Profkelly during the Winter '10 term at York University.

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Ch.18 - 18.2 o Species are the fundamental taxonomic units...

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