Frederick Griffith and Oswald Avery were key researchers in the discovery of DNA. Griffith was a British medical officer and geneticist. In 1928, in what is today known as Griffith's experiment, he discovered what he called a "transforming principle" that caused inheritance. Oswald and his colleagues, Colin MacLeod and Maclyn McCarty continued Griffith's research and discovered in 1944 that DNA is the material of which genes and chromosomes are made. All modern molecular biology has evolved from this discovery.
|Frederick Griffith||Oswald Avery|
|Date of birth||1879||October 21, 1877|
|Place of birth||Hale, England||Halifax, Canada|
|Died||1941||February 2, 1955|
|Known for||Discovery of pneumococcal transformation||Discovering that DNA transmits heredity|
|Introduction (from Wikipedia)||Frederick Griffith was a British medical officer and geneticist. In 1928, in what is today known as Griffith's experiment, he discovered what he called a transforming principle, which is today known to be DNA.||Oswald Theodore Avery was a Canadian-born American physician and medical researcher. He is best known for his discovery in 1944 that DNA is the material of which genes and chromosomes are made.|
|Institutions||Ministry of Health||Rockefeller University Hospital|
|Fields||physician, pathologist, bacteriologist||molecular biology|
Working for the British Ministry of Health, Griffith was trying to make a vaccine to prevent pneumonia infections in the "Spanish flu" influenza pandemic after World War I, by using two strains of the Streptococcus pneumoniae bacterium. The smooth strain (S strain) had a polysaccharide capsule and was virulent when injected, causing pneumonia and killing mice in a day or two. The rough strain (R strain) did not cause pneumonia when injected into mice, since it lacked a capsule. When the virulent S strain was heated to kill it, and then injected into mice, it produced no ill effects. However, when dead S strain mixed with live R strain was injected into the mouse, the R/S mouse died.
While neither (heat-killed S strain or live R strain) alone harmed the mice, the combination was able to kill its host. Griffith isolated both strains of pneumococcus from the blood of these dead mice. He concluded that the type II-R had been "transformed" into the lethal III-S strain by a "transforming principle" that was somehow part of the dead III-S strain bacteria.
See Also: Early DNA Research (YouTube video)
Avery, MacLeod and McCarty continued Frederick Griffith's research with their own set of experiments in the 1930s and 40s, publishing their results in 1944. They used techniques to remove various organic compounds from bacteria to test how characteristics were inherited. After removing certain organic compounds, if the remaining organic compounds were still able to cause R strain bacteria to transform then the substances removed couldn't be the carrier of genes. They thus tried to identify the source of inheritance through the method of elimination.
They first removed the large cellular structures from the S strain bacteria. Then they treated the bacteria with protease enzymes, which removed the proteins from the cells. The remainder of the S strain bacteria was then placed with R strain bacteria. But the R strain bacteria still transformed, proving that proteins did not carry the genes for causing the disease. When the remnants of the R strain bacteria were treated with a deoxyribonuclease enzyme which removed the DNA, the R strain bacteria no longer transformed. This indicated that DNA was the carrier of genes in cells.