Fig. 3. Maximum-likelihood phenogram based on a DNA alignment of the coding sequence of glutamine synthetase genes in vertebrates. The nucleotide alignment used (available upon request) is identical in form to the amino acid alignment (Fig. 2). Nomenclature of genes is similar to that used in Fig. 2, except that unique GenBank accession numbers have been added to the sequences reported to assist comparison with other papers that may use slightly different nomenclature schemes (i.e. Walsh et al., 2003). Genes coding for mitochondrial isozymes are underlined. Bootstrap values above 50%, based on 200 bootstraps, are placed at the appropriate nodes.