THE genetic code used by all life today may have evolved from two simpler codes in the distant past. If so, traces of ancient genes using these earlier codes might be lurking in the plethora of apparently useless “junk” DNA that litters almost all genomes.
The genetic language is made up of three-letter “words”, known as codons, which each specify a particular protein building block, or amino acid. Since each letter in the codon can be any of four different bases, there are 64 possible combinations (see Table). But the code specifies only 20 amino acids, and this has…
