Abstract
We conducted detailed analyses of recently emerged animal duplogs (intra-species paralogs). Genome data of three vertebrate species (human, mouse, and zebrafish), Caenorhabditis elegans, and two Drosophila species were used. Duplication events were classified into different age groups according to synonymous distance (dS) between duplogs. We observed following general tendencies: (A) Inverted duplogs account for 20 to 50% of intra-chromosomal duplogs depending on species, and about half of most distant 25% duplogs; (B) Composition of physical distances and that of relative orientations remain almost unchanged; (C) Even youngest age-group (dS<0.01) shows physical relationship compositions similar to those in entire set. These observations suggest that intra-chromosomal duplogs with fairly long distances and random relative orientations were directly generated, rather than resulting from tandem duplications and subsequent genomic rearrangements. We term this duplication mode 'fourth mode', as it is different from three well-known modes of gene duplication; tandem duplication, retrotransposition, and genome duplication.