After 1944, a remarkable set of discoveries established the overall shape of modern molecular biology and most famous of all was the discovery of the three dimensional structure of DNA: the famous double helix, which explained how the substance could act as the genetic material. ‘Genes as DNA’ describes the complex structure of genes and explains the terms ‘genome’ and ‘genomics’. In the 1980s and 1990s the complex mechanisms by which genes control embryonic development were discovered. The complete sequencing of a typical human genome was started in the late 1990s and achieved in 2003. It showed that the genome of human beings contains about three billion base pairs of DNA.