Reconstructing the gene map of the vertebrate ancestor

Abstract

Assembly of fish gene maps, while still in its infancy, has permitted insightful comparisons to be made with gene maps of other vertebrates, particularly mammals. From the limited data available from salmoniform, perciform, cyprinodontiform, and siluriform fishes, it appears that linkage groups are highly conserved in teleosts, and perhaps have diverged less from arrangements of vertebrate ancestors than have syntenic groups of other vertebrate species. The expression of duplicate genes for a large number of enzyme systems in fishes has been instrumental in identification of chromosomes or chromosome segments almost certainly derived by chromosome duplications in vertebrate ancestors. A composite teleost linkage map, for example, evidences linkage of duplicate glucosephosphate isomerase, pyruvate kinase, isocitrate dehydrogenase, and glutamate‐oxaloacetate transaminase genes on two chromosomes which, when linkage of orthologues of alpha‐mannosidase and peptidase D are included, appear to be homologues of segments of human chromosomes 15 and 19. Chromosomal locations of Iactate dehydrogenase, malate dehydrogenase, glyceraldehyde‐3‐phosphate dehydrogenase, and cytosolic aminopeptidase duplicates suggest that all the genes listed derive from genes which were syntenic on one of three chromosome pairs in a vertebrate ancestor which have undergone three chromosome duplication events, probably by tetraploidization, to produce the genome of the first vertebrate.