19 - PROKARYOTIC DIVERSITY BIOL 4125 SPRING 2009 LECTURE 19...

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PROKARYOTIC DIVERSITY BIOL 4125 SPRING 2009 LECTURE 19 Deep-branching Bacteria
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Portion of the only figure in Darwin’s Origin of Species Darwin used a tree to represent the divergence of variants within a species, showing successively more difference in a single lineage ( a 1 through a 10 ) and splitting into multiple lineages ( m, s, i , etc.), some of which will become new species. “Limbs divided into great branches . ..were themselves once, when the tree was small, budding twigs; and this connection of the former and present buds by ramifying branches may well represent the classification of all extinct and living species in groups subordinate to groups"
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The earliest common ancestor to all primates? A group of organisms is said to have common descent if they have a common ancestor • Collectively, a group of species with common descent will share common traits and tendencies. • For example, all primates posses the following adaptations: - move limbs in various directions - grasping power of the hands and feet - retention of the clavicle - flexibility of the spine • Lemurs were geographically isolated and are considered ‘primitive’ members of the primate order. • They lack certain physical attributes that emerged in later developing primates and retained characteristics lost by later evolving primates. • They provide important clues on the nature of the last common ancestor of all primates. news.bbc.co.uk/1/hi/sci/tech/1935558.stm
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Our current understanding of the phylogeny of Bacteria is based on the comparison of the highly conserved 16S rRNA gene Main radiation; predominantly mesophiles Early, “primitive” (short branch length), mostly thermophilic species
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there are limitations and considerations when using a single gene to infer the phylogeny of the whole organism • Mutational saturation is a problem, due to their restricted lengths, i.e., further changes are as likely to make sequences more similar as they are to make them more different. - There are only 4 possible nucleotides. - The probability that two lineages will evolve the same nucleotide at the same site increases with the DNA substitution rate. - Referred to as long branch attraction. • There is heterogeneity in the rate of molecular evolution between organisms due to: - incident mutation during DNA duplication - metabolic environment having thermal or oxidative differences - efficiency or bias in mutation repair - recombination - generation times • Many genes give different phylogenies for the same organisms and almost certainly have been laterally transferred. “There is no compelling reason other than pride of place to chose
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19 - PROKARYOTIC DIVERSITY BIOL 4125 SPRING 2009 LECTURE 19...

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