ANCIENT LARGE-SCALE GENOME DUPLICATIONS - PHYLOGENETIC AND LINKAGE ANALYSES SHED LIGHT ON CHORDATE GENOME EVOLUTION

Paralogous genes from several families were found in four human chromo some regions (4p16, 5q33-35, 8p12-21, and 10q24-26), suggesting that t heir common ancestral region underwent several rounds of large-scale d uplication. Searches in the EMBL databases, followed by phylogenetic a nalyses, showed that cognates (orthologs) of human duplicated genes ca n be found in other vertebrates, including bony fishes. In contrast, w ithin each family, only one gene showing the same high degree of simil arity with all the duplicated mammalian genes was found in nonvertebra tes (echinoderms, insects, nematodes). This indicates that large-scale duplications occurred after the echinoderms/chordates split and befor e the bony vertebrate radiation. It has been suggested that two rounds of gene duplication occurred in the vertebrate lineage after the sepa ration of Amphioxus and craniate (vertebrates + Myxini) ancestors. Bef ore these duplications, the genes that have led to the families of par alogous genes in vertebrates must have been physically linked in the c raniate ancestor. Linkage of some of these genes can be found in the D rosophila melanogaster and Caenorhabditis elegans genomes, suggesting that they were linked in the triploblast Metazoa ancestor.