Watson and Crick and the Double Helix
Chromosomes are made up of both protein and DNA, and for some time, scientists did not know which of these macromolecules was responsible for inheritance.
In 1928, Frederick Griffith discovered the process of transformation—the process by which cells can take in, incorporate, and express foreign DNA—after noting that genetic information dead bacteria could be transferred to living bacteria. It wasn’t until 1944, however, that a group of researchers discovered that DNA was the molecule responsible for this transfer of genetic information. Finally, the Hershey-Chase experiment in 1952 also confirmed that it was DNA and not protein that was responsible for inheritance.
In 1953, what is perhaps the most well-known advance in genetics was made: James D. Watson and Francis Crick determined the structure of DNA. Crucial in this discovery was the research of a third scientist, Rosalind Franklin, who supplied x-ray crystallography work which allowed the duo to determine that DNA has a helical structure composed of two strands of DNA, each with a carbon-phosphate backbone, and pairs of nucleotides arranged like the rungs on a ladder.
Unfortunately, Rosalind Franklin has never received the credit she should have been entitled to for her role in Watson and Crick's discovery, and in fact it was not until well after her death that the importance of her work became public knowledge. It is entirely possible that had she not died at just 37, she would have been nominated for a Nobel Prize along with the famous duo (Nobel Prize rules do not allow posthumous nominations).
Determining the structure of DNA was particularly important because it suggested two crucial possibilities about genetic inheritance: first, that genetic information was carried by the sequence of nucleotides on the DNA strands, and second, that duplication of DNA could be achieved if the strands were unwound, and each single strand was used as a template for a new strand. Both of these possibilities turned out to be the case.