A universal homology: the genetic code

The translation between base triplets in the DNA and amino acids in proteins - the genetic code - is universal to all life, as can be confirmed, by isolating the mRNA for hemoglobin from a rabbit and injecting it into the bacterium Escherichia coli (pictured opposite). E. coli do not normally make hemoglobin, but when injected with the mRNA they make rabbit hemoglobin. The machinery for decoding the message must therefore be common to rabbits and E. coli; and if it is common to them it is a reasonable inference that all living things have the same code.