During the last 40 years or so there has been an exponential growth in our knowledge of biology and medicine and, within this period, several discoveries stick out as particularly important. The opening salvo for all later revolutionary developments was the clarification of the structure of DNA by Watson and Crick in the early 1950s. Another milestone was the breaking of the genetic code by Holley, Khorana and Nierenberg in the 1960s. Nowadays, most people know that DNA is made up from a double helix of deoxyribonucleic acid, where the genetic information is laid down in the sequence of the DNA building blocks, the nucleotides. Genes, as we now know, are in principle nothing other than sections of the chromosomal DNA harbouring, in the sequence of contiguous nucleotide triplets, the genetic information for the synthesis of proteins, as a rule one protein per gene.