Rate Variation Among Nuclear Genes and the Age of Polyploidy in Gossypium

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2003-01-01
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Senchina, David
Alvarez, Ines
Cronn, Richard
Liu, Bao
Rong, Junkang
Noyes, Richard
Paterson, Andrew
Wing, Rod
Wilkins, Thea
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Wendel, Jonathan
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Botany
The Botany Graduate Program offers work for the degrees Master of Science and Doctor of Philosophy with a graduate major in Botany, and minor work for students majoring in other departments or graduate programs. Within the Botany Graduate Major, one of the following areas of specialization may be designated: aquatic and wetland ecology, cytology, ecology, morphology, mycology, physiology and molecular biology, or systematics and evolution. Relevant graduate courses that may be counted toward completion of these degrees are offered by the Departments of EEOB and GDCB, and by other departments and programs. The specific requirements for each student’s course distribution and research activities are set by the Program of Study Committee established for each student individually, and must satisfy all requirements of the Graduate College (See Index). GRE (and if necessary, TOEFL) scores are required of all applicants; students are encouraged to contact faculty prior to application.
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Molecular evolutionary rate variation in Gossypium (cotton) was characterized using sequence data for 48 nuclear genes from both genomes of allotetraploid cotton, models of its diploid progenitors, and an outgroup. Substitution rates varied widely among the 48 genes, with silent and replacement substitution levels varying from 0.018 to 0.162 and from 0.000 to 0.073, respectively, in comparisons between orthologousGossypium and outgroup sequences. However, about 90% of the genes had silent substitution rates spanning a more narrow threefold range. Because there was no evidence of rate heterogeneity among lineages for any gene and because rates were highly correlated in independent tests, evolutionary rate is inferred to be a property of each gene or its genetic milieu rather than the clade to which it belongs. Evidence from approximately 200,000 nucleotides (40,000 per genome) suggests that polyploidy in Gossypium led to a modest enhancement in rates of nucleotide substitution. Phylogenetic analysis for each gene yielded the topology expected from organismal history, indicating an absence of gene conversion or recombination among homoeologs subsequent to allopolyploid formation. Using the mean synonymous substitution rate calculated across the 48 genes, allopolyploid cotton is estimated to have formed circa 1.5 million years ago (MYA), after divergence of the diploid progenitors about 6.7 MYA.

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This article is from Molecular Biology and Evolution 20 (2003): 633, doi:10.1093/molbev/msg065.

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