Technologies

Experiments with peas lead Austrian monk Gregor Mendel to discover that certain traits are inherited in varying proportions, depending on whether they are recessive or dominant.

Swiss physician Frederich Miescher isolates DNA from cells. Miescher calls it "nuclein." Later, it becomes known as nucleic acid.

German scientist Wilhelm Johannsen names the Mendelian unit of heredity "gene," from the Greek word, "give birth to."

British microbiologist Frederick Griffith's experiments with pneumococcus prove that a "transforming principle" allows genes to transfer from one bacterium to another.

American geneticists Oswald Avery, Colin MacLeod, and Maclyn McCarty prove that DNA is the "transforming principle"—the vehicle for passing hereditary information through generations.

Austrian-American biochemist Erwin Chargaff discovers equal amounts of adenine and thymine, and cytosine and guanine, a distinctive pattern of base-pairing regularities in DNA. In 1950 he publishes his findings.

American geneticists Alfred Hershey and Martha Chase demonstrate that only the DNA of a virus needs to enter a bacterium to infect it, proving that genes are made of DNA.

American biochemist Arthur Kornberg and Spanish born biochemist Severo Ochoa share the Nobel Prize in Physiology or Medicine for their discovery of polymerases in the biologic synthesis of deoxyribonucleic acid and ribonucleic acid.

South African chemist Sydney Brenner, French biologist François Jacob, and American geneticist Matthew Meselson show that short-lived RNA molecules, which they called messenger RNA (mRNA), carry the genetic instructions from DNA to structures in the cell called ribosomes, (the site of protein synthesis).

In 1953, James Watson and Frances Crick propose a three-dimensional model for the structure of DNA: a double helix molecule formed by two chains, each composed of alternating sugar and phosphate groups, connected by nitrogenous bases. Watson and Crick (with British biophysicist Maurice Wilkins) are awarded the 1962 Nobel Prize in Medicine or Physiology.

The Frances Crick Papers

Swiss molecular biologist Werner Arber shows how specialized enzymes can cut DNA into short strands. These enzymes are subsequently dubbed "restriction enzymes." In 1970, American molecular biologist Hamilton Smith and colleagues determine that restriction enzymes can cut DNA molecules at precise and predictable locations. Arber shares the 1978 Nobel Prize in Medicine or Physiology with Smith and American biologist Daniel Nathans.

In the 1960s and 1970s, British scientists Frederick Sanger and Alan Coulson, and Alan Maxam and Walter Gilbert in the United States, develop DNA sequencing techniques. Automated equipment makes DNA sequencing a speedy, routine laboratory procedure. Gilbert and Sanger win the 1980 Nobel Prize in Chemistry for their work.

American geneticist David Botstein, biochemist Ronald W. Davis, population geneticist Mark Skolnick, and biologist Ray White publish a paper on their theory that restriction fragment-length-polymorphisms (RFLPs) can be used to produce a linkage map of the human genome and to map the genes that cause disease in humans.

British geneticist Alec Jeffreys finds that multiple copies of short nucleotide sequences, 3 to 30 base pairs long, are repeated one after another, 20 to 100 times [e.g., GACTGACTGACT]. These groups of repeat sequences, called minisatellites or VNTRs (variable number of tandem repeats), are now known to be widely scattered throughout the human genome. The number of these regions at different loci are different in each individual.

Geneticist Alec Jeffreys develops short tandem repeat (STR) DNA typing, which the forensic community adopts as its standard.