After comparing the genomic sequences of the two yeast species Saccharomyces cerevisiae and Candida albicans, Seoighe et al. report in the December 19 Proceedings of the National Academy of Sciences that gene adjacencies have been broken as frequently by small inversions as by translocations or long-distance transpositions (Proc Natl Acad Sci USA 2000, 97:14433-14437). Only 9% of gene pairs that are adjacent in one species are conserved as adjacent in the other, and the number of orientation changes suggest that approximately 1,100 single gene inversions have occurred in the 140-330 million years since the two species diverged from each other. Using a model of the rearrangements, Seoighe et al. conclude that approximately equal numbers of linkages have been broken by small and large rearrangements. The mechanism behind the small inversions is unknown, but small inversions may be favored for either mechanistic reasons or because of...

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