AP BIOLOGY

Detailed explanation-1: -Many scientists contributed to the identification of DNA as the genetic material. In the 1920s, Frederick Griffith made an important discovery. He was studying two different strains of a bacterium, called R (rough) strain and S (smooth) strain. He injected the two strains into mice.

Detailed explanation-2: -Who first identified DNA? Although James Watson and Francis Crick determined the double-helical structure of DNA, DNA itself was identified nearly 90 years earlier by Swiss chemist Friedrich Miescher.

Detailed explanation-3: -Transformation in Bacteria In 1928, in an attempt to develop a vaccine against pneumonia, Frederick Griffith became the first to identify bacterial transformation, in which the form and function of a bacterium changes.

Detailed explanation-4: -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.

Detailed explanation-5: -These results suggested that DNA was the molecule responsible for transformation. Avery and his colleagues provided further confirmation for this hypothesis by chemically isolating DNA from the cell extract and showing that it possessed the same transforming ability as the heat-treated extract.