Genomic DNA fragments in exon 4 of chicken, goldfish and salmon visual
pigments were amplified by polymerase chain reaction, using oligonucl
eotide mixtures as primers, and hypothetical phylogenetic trees were d
rawn up from the deduced amino acid sequences. The results suggest tha
t vertebrate visual pigments have evolved along at least five lines, a
nd that these lines diverged from an ancestral gene before the bony fi
shes diverged from the rest of the higher vertebrates.