The evolutionary dynamics of eukaryotic gene order

In eukaryotes, unlike in bacteria, gene order has typically been assumed to be random. However, the first statistically rigorous analyses of complete genomes, together with the availability of abundant gene-expression data, have forced a paradigm shift: in every complete eukaryotic genome that has been analysed so far, gene order is not random. It seems that genes that have similar and/or coordinated expression are often clustered. Here, we review this evidence and ask how such clusters evolve and how this relates to mechanisms that control gene expression.