Evolution of gene order in the genomes of two related yeast species

Chances in gene order between the genomes of two related yeast species, Sac charomyces cerevisiae and Saccharomyces bayanus var. uvarum were studied. F rom the dataset of a previous low coverage sequencing of the S. bayanus var . uvarum genome, 35 different synteny breakpoints between neighboring genes and two cases of local gene inversion were characterized in detail. The nu mber and the type of the chromosomal rearrangements that have lead to these differences were identified. We show that evolution of gene order in the g enomes of these two yeast species is driven mainly by gene duplication onto different chromosomes followed by differential loss of the repeated copies . In addition, local gene inversions also would result from a mechanism of gene duplication, but in an inverted orientation, followed by loss of the o riginal copy. The identification of traces of anciently duplicated genes, c alled relics, show that the loss of duplicates is more frequently caused by the accumulation of numerous mutations in one of the two copies than by DN A deletion. Surprisingly, gross chromosomal rearrangements such as transloc ations have only a minor effect on gene order reshuffling as they account f or < 10% of the synteny breakpoints.