Linked evolution

There is more variation in the rate of protein evolution than is expected by chance, although this variation is not caused by slower evolution of essential genes. In the 19 October Nature Williams and Hurst report that one determinant of evolution rates is gene position: the proteins of linked genes evolve at similar rates (Nature 2000, 407:900-903). The major cause of this phenomenon does not seem to be varying concentrations of mutation-sensitive CpG dinucleotides. The real cause may be the clustering of genes of comparable function, or the variation in recombination frequencies at different chromosomal sites.