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dna double helix While DNA (DeoxyriboNucleic Acid) was discovered in 1868, it wasn't recognized as genetic material until almost a century later.

DNA was discovered by a Swiss medical student named Johann Friedrich Miescher, who found it when working with white blood cells that he took from pus drained out of a surgical wound.  He determined that the nuclein was rich in phosphorous and was also acidic.  That's why it was named nucleic acid, a name DNA still has today.

While Miescher found DNA, it wasn't until 84 years later, in the early 1950s, that scientists recognized it as genetic material.  Prior to that, everyone thought DNA, with its four bases, was too simple to be the genetic material.

In 1920, Frederick Griffith found that bacteria could acquire something from each other to turn harmless bacteria into deadly bacteria, though he wasn't sure what.  A team led by scientist Oswald Avery determined that DNA caused the change.

However, the medical community was skeptical until 1952, when Alfred Hershey and Martha Chase, who were working with a specific virus, found that the viruses injected only DNA into the bacterial cell to infect it.

Another scientist who contributed to what we know about DNA was Erwin Chargaff.  He found that when all DNA was broken down into components, the amount of guanine fluctuated from one organism to the other but was always equal to the amount of cytosine.  Also, the amount of adenine was the same as the amount of thymine.

American geneticist James Watson and English physicist Francis Crick, with much help from a scientist named Rosalind Franklin, figured out why the ratios were important to the structure of DNA.  Franklin's data on the shape of the DNA molecule revealed its structure of the double helix; in a great controversy, Watson and Crick scooped Franklin's information and, using Chargaff's rules, cracked the DNA structure code.

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The Discovery of DNA