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In 1950, biochemist Erwin Chargaff found that the arrangement of nitrogen bases in DNA varied widely, but the amount of certain bases always occurred in a one-to-one ratio. These discoveries were an important foundation for the later description of DNA. In the early 1950s, the race to discover DNA was on.

Since the beginning of human history, people have wondered how traits are inherited from one generation to the next.

Because of this possibility, debate over DNA's role continued until 1952, when Alfred Hershey and Martha Chase used a different approach to conclusively identify DNA as the genetic material.

The way in which traits are passed from one generation to the next-and sometimes skip generations-was first explained by Gregor Mendel. By experimenting with pea plant breeding, Mendel developed three principles of inheritance that described the transmission of genetic traits, before anyone knew genes existed.

Earlier work had shown that DNA is composed of building blocks called nucleotides consisting of a deoxyribose sugar, a phosphate group, and one of four nitrogen bases — adenine (A), thymine (T), guanine (G), and cytosine (C). Phosphates and sugars of adjacent nucleotides link to form a long polymer.

For multiple decades following Miescher's discovery, most scientists continued to believe that protein, not DNA, was the carrier of hereditary information. This changed in 1944, when biologist Oswald Avery performed a series of groundbreaking experiments with the bacteria that cause pneumonia.

In a very simple experiment, Oswald Avery's group showed that DNA was the "transforming principle." When isolated from one strain of bacteria, DNA was able to transform another strain and confer characteristics onto that second strain. DNA was carrying hereditary information.

These four scientists—Crick, Franklin, Watson, and Wilkins—codiscovered the double-helix structure of DNA, which formed the basis for modern biotechnology. At King's College London, Rosalind Franklin obtained images of DNA using X-ray crystallography, an idea first broached by Maurice Wilkins.