In a new article in Genome Biology, Laurence Hurst finds that asking the same question in different organisms can arrive at strikingly different answers.

Hurst, who is a Professor of Evolutionary Genetics at the University of Bath, had previously shown that clustering of co-expressed genes in the yeast genome is evolutionarily conserved. His work on yeast led him to wonder whether the same story holds true in other organisms.

Fortunately, the vast quantity of high quality genomic data that is now being generated has allowed him to ask whether gene order is also conserved in the fruit fly Drosophila melanogaster. Perhaps surprisingly, Hurst (together with lab member Claudia Weber) found that clustering of co-expressed genes in Drosophila melanogaster did not appear to be conserved. In fact, the opposite pattern seemed to be true, in that neighbouring genes with similar expression patterns had an increased likelihood of becoming rearranged.

This phenomenon may be explained by a scenario in which the closeness of two genes is the reason for their co-expression, because they are likely to be exposed to the expression machinery at the same time. This co-expression would likely be unhelpful to the cell and so may be selected against during evolution.

The question of why yeast and Drosophila melanogaster tell a different evolutionary history of gene clusters remains open – but the study underscores the importance of testing genomic theories in different organisms.