A tentative schematic view of the migration of OR genes in an “out of chromosome 11” scenario, based mainly on the cluster composition analysis (see text and Fig. 7 for details). The proposed steps, in rough chronological order, are (1) a duplication on chromosome 11 that resulted in the formation of the first class II cluster out of an original class I cluster (thick cyan); (2) a duplication that led to the formation of a cluster on chromosome 1, most likely in the framework of a whole genome diploidization (thick magenta); (3) internal duplications within chromosome 11 (thin green), and expansion from chromosome 1 onto a number of other chromosomes (thick green); (4) additional isolated duplications (thin black); gene scattering of family 4 (red “radio waves”) and family 7 (blue “radio waves”). Only the generation of clusters larger than five members is explicitly shown. The small red histograms to the right of the chromosomal bands indicate OR gene cluster locations, with the area proportional to cluster size (see http://bioinfo.weizmann.ac.il/HORDEfor details).
