Tempo and Mode in Evolution Genetics and Paleontology 50 Years After Simpson (1995) / Chapter Skim
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The History of a Genetic System
The History of a Genetic System
Pages 287-298
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From page 287... ...
George Gaylord Simpson published Tempo and Mode in Evolution (1944) , bringing paleontology and the concepts of macroevolution into the modern synthesis of evolutionary theory.
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pseudoobscura gene arrangements examined in the present study. Stebbins supported Epling's hypothesis and argued that the inversion system was quite old, while Mayr disagreed with Epling and favored a more recent origin of the distribution pattern.
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Three SC strains from Michoacan, Mexico, were added to the original RSP data set: strain MEX z67w, strain MEX z53y, and strain MEX z13w. Restriction mapping of these strains was carried out as described previously (Aquadro et al., 1991~.
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tree derived from RSP data, we followed the advice kindly given to us by Walter Fitch. First, "1" and "0" in the data set were replaced with "A" and "T." respectively.
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A phylogenetic analysis of each flanking region generated the same branching topology, so we combined the two regions (Figure 2~. In the deduced phylogeny, the TL arrangement splits off early from the SC-ST group, a finding concordant with the results of the previous RSP data analysis (Aquadro et al., 1991~.
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These regions appear to be functionally unconstrained, with sequence divergence levels comparable to that of the RSP data. This makes them useful for phylogenetic analysis.
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First, we added three more SC strains to assure that SC was adequately represented, since the original data set contained only two SC strains. Second, the data were analyzed with the NI, MP, and ML methods.
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, with very short branch lengths. The rest of the SC strains join either the TL or the ST arrangements.
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This discrepancy is due partially to the addition of three more SC strains, after which the scattering of SC arrangements throughout the phylogeny becomes obvious, and partially to the varying rate of evolution among different arrangements, combined with the low level of observed divergence (at most 4% )
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. pers~m~ Is SC CH SC miranda FIGURE 7 The two possible scenarios showing the relationships among all gene arrangements represented in the RSP data set.
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pseudoobscura, a molecular evolutionary approach has brought us close to an understanding of the origin of this genetic system. SUMMARY Although the chromosomal polymorphism for inversions in Drosophila pseudoobscura is one of the best studied systems in population genetics, the identity of the ancestral gene arrangement has remained unresolved for more than 50 years.
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(1945) in Symposium on age of the distribution pattern of the gene arrangements in Drosophila pseudoobscura.
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