1950
Erwin Chargaff discovered the base-pairing regularities of nucleic acids that provided one of the key steps in developing a structural model for DNA. Chargaff's best known achievement was to show that in DNA the number of guanine units equals the number of cytosine units and the number of adenine units equals the number of thymine units. This strongly hinted towards the base pair makeup of the DNA.
At that time, many people and scientist thought of DNA being a simple complex. Many people thought the chromosome's proteins, not its DNA, encoded the genes. Chargaff thought different and decieded to act upon his "hunch." Chargaff could precisely measure the amount of each base in a DNA sample. The results overturned the tetranucleotide hypothesis: The bases were not present in equal quantities and they varied from organism to organism. The DNA molecule wasn't so simple after all.
Chargaff also noticed that no matter where DNA came from – yeast, people or salmon – the number of adenine bases always equaled the number of thymine bases and the number of guanine always equaled the number of cytosine bases. He published a review of his experiments in 1950, calling the ratios – later known as Chargaff's Rules – "regularities."
