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Oswald Avery
A Canadian-born American named Oswald Avery showed that DNA is responsible for the transmission of
heritable characteristics. Avery moved from Canada to New York City in 1887. He attended Colgate University and in
1904 received his medical degree from the College of Physicians and Surgeons at Columbia University. He practiced
medicine for several months before he became more interested in the transmission of infectious diseases. In 1913, Avery
arrived at Rockefeller Institute, where he worked as a bacteriologist for over 43 years.
Avery and his co-workers studied the life cycle and chemical make-up of Diplococcus pneumoniae , or
pneumococci, a species of bacteria that causes pneumonia. Avery's interest was sparked by British microbiologist
Frederick Griffith's work with the same bacteria (Station 1). In 1928, Griffith described an experiment in which he injected
mice with a mixture of a harmless strain of living pneumococci and the dead remains of a virulent strain of the bacteria.
The mice died from infection by the live organisms of the virulent strain, though the organisms had been dead when they
were administered. Because of Griffith’s study, Avery began to focus on transformation—the process by which heritable
characteristics of one species are incorporated into another different species.
In 1944, Avery and his colleagues identified the molecule that transformed the R strain of bacteria into the S strain
(from Griffith’s experiment). Avery isolated different macromolecules, such as DNA, protein, and lipids, from killed S
cells. Then he exposed live R cells to the macromolecules separately. When the live R cells were exposed to the S strain
DNA, they were transformed into S cells. Avery concluded that when the S cells in Griffith’s experiments were killed, DNA
was released. Some of the bacteria incorporated this DNA into their cells, and this changed the bacteria into S cells.
Avery’s conclusions were not widely accepted by the scientific community, and many biologists continued to question and
experiment to determine whether proteins or DNA were responsible for the transfer of genetic material.
This experiment, first published in 1944, was extremely important because, for the first time, scientists had
proven that DNA controls the development of a cellular feature. It also implicated DNA as the basic genetic material of
cells and stimulated James Watson and Francis Crick to later discover its structure and method of replication. Today we
understand that DNA is the fundamental molecule involved in heredity.
Watson and Crick
Francis Harry Compton Crick was born on 8 June 1916 near Northampton. He studied physics at
University College, London, and during World War Two worked for the Admiralty on the development of
mines. He changed from physics to biology and in 1947 began to work at Cambridge University. By 1949,
he was working at the Medical Research Council unit at the Cavendish Laboratory in Cambridge. In 1951,
an American student, James Watson, arrived at the unit and the two began to work together.
James Dewey Watson was born on 6 April 1928 in Chicago and studied at the universities of Chicago,
Indiana and Copenhagen. He then moved to Cambridge University. Watson and Crick worked together on
studying the structure of DNA (deoxyribonucleic acid), the molecule that contains the hereditary
information for cells.
At that time Maurice Wilkins and Rosalind Franklin, both working at King's College, London, were using Xray diffraction to study DNA. Crick and Watson used their findings in their own research. In April 1953,
they published the news of their discovery, a molecular structure of DNA based on all its known features the double helix. Their model served to explain how DNA replicates and how hereditary information is
coded on it. This set the stage for the rapid advances in molecular biology that continue to this day.
Watson, Crick and Wilkins shared the Nobel Prize in Medicine in 1962. Franklin had died in 1958 and,
despite her key experimental work, the prize could not be received posthumously. Crick and Watson both
received numerous other awards and prizes for their work.
Francis Crick continued to work in genetics and then moved into brain research, becoming a professor at
the Salk Institute for Biological Studies in California. He died on 28 July 2004.
From 1988 to 1992, James Watson directed the Human Genome Project at the American National
Institutes of Health. He was instrumental in obtaining funding for the project and in encouraging
cooperation between governments and leading scientists.
Born: London, England, July 25, 1920
Died: London, England, April 16, 1958
Pioneer Molecular Biologist
There is probably no other woman scientist with as much controversy
surrounding her life and work as Rosalind Franklin. Franklin was
responsible for much of the research and discovery work that led to the
understanding of the structure of deoxyribonucleic acid, DNA. The story
of DNA is a tale of competition and intrigue, told one way in James
Watson's book The Double Helix, and quite another in Anne Sayre's
study, Rosalind Franklin and DNA. James Watson, Francis Crick, and Maurice Wilkins received a Nobel Prize
for the double-helix model of DNA in 1962, four years after Franklin's death at age 37 from ovarian cancer.
As a child, Franklin excelled at science and attended one of the few girls' schools in London that taught physics
and chemistry. When she was 15, she decided to become a scientist. Her father was decidedly against higher
education for women and wanted Rosalind to be a social worker. Ultimately he relented, and in 1938 she
enrolled at Newnham College, Cambridge, graduating in 1941. She then earned a doctorate in physical
chemistry, from Cambridge University in 1945.
After Cambridge, she spent three productive years (1947-1950) in Paris at the Laboratoire Central des Services
Chimiques de L'Etat, where she learned X-ray diffraction techniques. In 1951, she returned to England as a
research associate in John Randall's laboratory at King's College, London.
It was in Randall's lab that she crossed paths with Maurice Wilkins. She and Wilkins led separate research
groups and had separate projects, although both were concerned with DNA. When Randall gave Franklin
responsibility for her DNA project, no one had worked on it for months. Wilkins was away at the time, and
when he returned he misunderstood her role, behaving as though she were a technical assistant. Both scientists
were actually peers. His mistake, acknowledged but never overcome, was not surprising given the climate for
women at the university then. Only males were allowed in the university dining rooms, and after hours
Franklin's colleagues went to men-only pubs.
But Franklin persisted on the DNA project. J. D. Bernal called her X-ray photographs of DNA, "the most
beautiful X-ray photographs of any substance ever taken." Between 1951 and 1953 Rosalind Franklin came
very close to solving the DNA structure. She was beaten to publication by Crick and Watson in part because of
the friction between Wilkins and herself. At one point, Wilkins showed Watson one of Franklin's
crystallographic portraits of DNA. When he saw the picture, the solution became apparent to him, and the
results went into an article in Nature almost immediately. Franklin's work did appear as a supporting article in
the same issue of the journal.
A debate about the amount of credit due to Franklin continues. What is clear is that she did have a meaningful
role in learning the structure of DNA and that she was a scientist of the first rank. Franklin moved to J. D.
Bernal's lab at Birkbeck College, where she did very fruitful work on the tobacco mosaic virus. She also began
work on the polio virus. In the summer of 1956, Rosalind Franklin became ill with cancer. She died less than
two years later.