Copy correction and concerted evolution in the conservation of yeast genes.

The yeast Saccharomyces cerevisiae and other members of the genus Saccharomyces are descendants of an ancient whole-genome duplication event. Although most of the duplicate genes have since been deleted, many remain, and so there are many pairs of related genes. We have found that poorly expressed genes diverge rapidly from their paralog, while highly expressed genes diverge little, if at all. This lack of divergence of highly expressed paralogous gene pairs seems to involve gene correction: one member of the pair "corrects" the sequence of its twin, and so the gene pair evolves as a unit. This correction presumably involves gene conversion and could occur via a reverse-transcribed cDNA intermediate. Such correction events may also occur in other organisms. These results support the idea that copies of poorly expressed genes are preserved when they diverge to take on new functions, while copies of highly expressed genes are preserved when they are needed to provide additional gene product for the original function.