Duplication of a portion of human chromosome 20q containing Topoisomerase (Top1)and Snail genes provides evidence on genome expansion and the radiation of teleost fish

Abstract

Zebrafish has two duplicate copies of many genes present in single copy in the human genome. Most gene duplicates map in duplicate chromosome segments, suggesting that they are the remnants of a whole genome duplication event. When did this event occur? To address this question, we mapped zebrafish orthologues of genes on human chromosome 20 (Hsa20). The results showed that LG11 and LG23 contain many orthologues of Hsa20 loci, including duplicates of SNAIL, TOPOISOMERASE-1, and KRML. Phylogenetic analysis showed that these chromosome segments were duplicated before the divergence of Cypriniform and Tetraodontiform fishes, as would be predicted by the hypothesis that a genome duplication event happened before the teleost radiation. Because differential loss of gene duplicates can facilitate reproductive isolation, and because gene duplication can foster the evolution of developmental innovations, we suggest the hypothesis that genome duplication in ray fin fish facilitated the teleost radiation, an explosion of diversity that produced half of all vertebrate species.