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Aromatic amino acid hydroxylase (AAAH) genes and insulin-like genes form part of an extensive paralogy region shared by human chromosomes 11 and 12, thought to have arisen by tetraploidy in early vertebrate evolution. Cloning of a complementary DNA (cDNA) for an amphioxus (Branchiostoma floridae) hydroxylase gene (AmphiPAH) allowed us to investigate the ancestry of the human chromosome 11/12 paralogy region. Molecular phylogenetic evidence reveals that AmphiPAH is orthologous to vertebrate phenylalanine (PAH) genes; the implication is that all three vertebrate AAAH genes arose early in metazoan evolution, predating vertebrates. In contrast, our phylogenetic analysis of amphioxus and vertebrate insulin-related gene sequences is consistent with duplication of these genes during early chordate ancestry. The conclusion is that two tightly linked gene families on human chromosomes 11 and 12 were not duplicated coincidentally. We rationalize this paradox by invoking gene loss in the AAAH gene family and conclude that paralogous genes shared by paralogous chromosomes need not have identical evolutionary histories.

Original publication




Journal article


Mol Biol Evol

Publication Date





1373 - 1380


Amino Acid Sequence, Animals, Base Sequence, Caenorhabditis elegans, Cattle, Chickens, Chordata, Nonvertebrate, Chromosome Mapping, Cloning, Molecular, DNA, Complementary, Drosophila melanogaster, Evolution, Molecular, Fishes, Gene Duplication, Humans, Insulin-Like Growth Factor I, Insulin-Like Growth Factor II, Mice, Molecular Sequence Data, Multigene Family, Neuropeptides, Phenylalanine Hydroxylase, Phylogeny, Quail, Rabbits, Rats, Sequence Homology, Nucleic Acid, Tryptophan Hydroxylase, Tyrosine 3-Monooxygenase, Xenopus laevis