DNA, or Deoxyribonucleic acid, is the helical macromolecule which encodes the genetic information that participates in cellular growth and development at the molecular level. (Source: R. Gerber, Vibrational Medicine, Glossary).

"DNA is the abbreviation for Deoxyribonucleic Acid, which is a compound found in chromosomes and consists of a long chain molecule comprising many repeated and varied combinations of four nucleotides, one of which is the sugar deoxyribose; subdivisions of the molecule are believed to be the genes. DNA is the major repository of genetic information." (Lyssa Royal & Keith Priest, The Prism of Lyra)

All life-forms are DNA-based, that is: their genetic template is stored in their DNA.
Research by Ilya Prigogine proved that as soon as the elements for DNA are available in the universe, strands of DNA come into existence, thus proving that the laws of Entropy (Chaos rules, no structure can occur by itself, unless it is by chance) do not apply to life in the universe.

When it comes to human galactic history, DNA plays an important part too. Several humanoid species that have evolved further that earth humans have, are said to have twelve-strand DNA, instead of the two-strand helix that we do have now. Several authors, like e.g., Barbara Marciniak, point out that genetic manipulation in the Atlantean era by extraterrestrials, stripped our DNA down to a two-strand DNA, instead of the twelve-strand helix we had before. This was done to slow down the evolution of the Earth human species. In the near future, however, the earth human race would start displaying twelve-strand DNA again.