Superoxide dismutase tree. The amino acid sequences (back translated to ambiguous codons) were fit most parsimoniously to this tree, which is 1984 nucleotide substitutions long by the method of Fitch (1971) and Fitch and Farris (1974). It is not the most parsimonious tree, which was not used for reasons discussed in Results. Part C of the figure shows that the Cu,Zn SOD gene became duplicated early in plant evolution, at least before the divergence of gymnosperms and angiosperms. The GenBank numbers for these sequences are as follows: A00512, human-1 (Homo sapiens); S01134, rabbit (Oryctolagus cuniculus); P07632, rat-1 (Rattus norvegicus); JQ0915, (Continued) mouse (Mus musculus); P08294, human-2; X68041, rat-2; A00514, pig (Sus scrofa); A00513, bovine (Bos primigenius taurus); P09670, sheep (Ovis aries); A00515, horse (Equus caballus ); S05021, African clawed toad-A (Xenopus laevis); S05022, African clawed toad-B; S09568, African clawed toad-A P03946, swordfish (Xiphias gladius); S04623, blue shark (Prionace glauca); S84896, scots pine-1 (Pinus sylvestris); S00999, rice-1 (Oryza sativa); D01000, rice-2; A29077, maize (Zea mays); A25569, white cabbage (Brassica oleracea); X60935, Arabidopsis thaliana; X73139, sweet potatoes (Ipomoea batatas); S08350, tomato-1 (Lycopersicon esculentum); P22233, spinach-1 (Spinacia oleracea); M63003, garden pea-1 (Pisum sativum); S84902, scots pine-2; JS0011, spinach-2; S12313, garden pea-2; S08497, tomato-2; P10792, garden petunia (Petunia hybrida); M58687, Neurospora crassa; A36171, Saccharomyces cerevisiae (yeast); X66722, Schizosaccharomyces pombe (yeast); X57105, Onchocerca volvulus-1 (nematode); Z27080, Caenorhabditis elegans-1 (nematode); L20135, Caenorhabditis elegans-2; L13778, Onchocerca volvulus-2; M68862, polyhedrosis virus; A37019, Schistosoma mansonii -1 (liver fluke); M86867, Schistosoma mansonii-2; M84013 and M84012, Haemophilus parainfluenza; M55259, Caulobacter crescentus (bacterium); A00519, Photobacterium leiognathi (bacterium); A33893, Brucella abortus (bacterium). In part B, D. stands for Drosophila.