title: Extraordinary conservation of entire chromosomes in insects over long evolutionary periods.
abstract: Comparison of the genomes of different Drosophila species has shown that six different chromosomes, the so-called ''Muller elements," constitute the building blocks for all Drosophila species. Here, we confirm previous results suggesting that this conservation of the Muller elements extends far beyond Drosophila, to at least tephritid fruit flies, thought to have diverged from drosophilids 60-70 mYr ago. Less than 10 percent of genes differ in chromosome location between the two insect groups. Within chromosomes, however, the order is highly scrambled, as expected from the comparison between Drosophila species. The data also support the notion that the sex chromosomes of tephritid flies originated from an ancestor of the dot chromosome 4 of Drosophila. Overall, therefore, no new chromosome has been created for perhaps a billion generations over the two evolutionary lines. This stability at the chromosome level, which appears to extend to all Diptera including mosquitoes, is in stark contrast to other groups such as mammals, birds, fish and plants, in which chromosome numbers and organization vary enormously among species that have diverged over much fewer generations.
authors.affiliation: Evolution and Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia. j.sved@unsw.edu.au.
authors.forename: John A
authors.initials: JA
authors.lastname: Sved
authors.affiliation: NSW Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Menangle, NSW 2568, Australia.
authors.forename: Yizhou
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Evolution and Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
authors.forename: Deborah
authors.initials: D
authors.lastname: Shearman
authors.affiliation: Evolution and Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
authors.forename: Marianne
authors.initials: M
authors.lastname: Frommer
authors.affiliation: Evolution and Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
authors.forename: A Stuart
authors.initials: AS
authors.lastname: Gilchrist
authors.affiliation: Evolution and Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
authors.forename: William B
authors.initials: WB
authors.lastname: Sherwin
mesh_terms: D000818:Animals; D059006:Chromosomes, Insect; D004175:Diptera / Q000235:genetics*; D004330:Drosophila / Q000235:genetics; D019143:Evolution, Molecular; D012730:Sex Chromosomes / Q000235:genetics; D033621:Tephritidae / Q000235:genetics
keywords: Chromosomal evolution; drosophila; evolutionary genomics; insects; molecular evolution; tephritids