Vertebrate genome evolution: a slow shuffle or a big bang?

In vertebrates it is often found that if one considers a group of genes clu stered on a certain chromosome, then the homologues of those genes often fo rm another cluster on a different chromosome. There are four explanations, not necessarily mutually exclusive, to explain how such homologous clusters appeared. Homologous clusters are expected at a low probability even if ge nes are distributed at random. The duplication of a subset of the genome mi ght create homologous clusters, as would a duplication of the entire genome . Alternatively, it may be adaptive for certain combinations of genes to cl uster, although clearly the genes must have duplicated prior to rearrangeme nt into clusters. Molecular phylogenetics provides a means to examine the o rigins of homologous clusters, although it is difficult to discriminate bet ween the different explanations using current data. However, with more exte nsive sequencing and snapping of vertebrate genomes, especially those of th e early diverging chordates, it should soon become possible to resolve the origins of homologous clusters. BioEssays 21:697-703, 1999. (C) 1999 John W iley & Sons, Inc.