Heredity is a molecule
DNA is the hereditary material of cellular life. Its double helix stores sequence information that is replicated and transcribed.
Avery, MacLeod, and McCarty showed in 1944 that a purified nucleic acid could transform pneumococcus. Hershey and Chase (1952) showed that phage DNA, not protein, enters the bacterial cell. The gene had an address.
Watson and Crick, using Franklin and Wilkins’s X-ray data, proposed the double helix in 1953. Base pairing explained both storage and copying. The code that maps triplets of bases to amino acids was worked out in the 1960s.
RNA viruses and prions are exceptions that prove the rule: information can ride on other molecules, but cellular life on Earth uses DNA as the archive. Sequencing turned ancestry into a readable text.
Caveats
- Epigenetic marks modify expression without changing sequence; they are important, and they are not a second genetic code that replaces DNA.
- Some viruses use RNA genomes.
Sources
- 1Watson J. D., Crick F. H. C.. Molecular Structure of Nucleic Acids. Nature 171, 1953.
- 2Avery O. T., MacLeod C. M., McCarty M.. Studies on the Chemical Nature of the Substance Inducing Transformation. Journal of Experimental Medicine 79, 1944.