Aka, deoxyribonucleic acid (DNA) is the genetic material! This journal article, published in 1952 by Alfred Hershey and Martha Chase, is a landmark discovery in molecular biology. I won't go into the gritty details, but I will offer some background and the basic gist of the experiment. (FYI, it's not the anniversary of its publication or anything--I'm just really excited that the .pdf is available online for free :-) )
At the time, no one knew exactly what passed on genetic information. By the 1950s, it was between DNA and proteins, and most scientists figured the latter were the molecules of life. It made the most sense, since proteins are far more complex than DNA--proteins can be made up of up to 20 different amino acids, whereas there are only four nucleic acids in DNA.
Hershey and Chase wanted to see what a virus used to infect bacteria (the "infectious material"). They labeled the proteins in one batch of virus with radioactive sulfur, and the DNA in another batch with radioactive phosphorus. They let the viruses hang out with the bacteria for a little while, then tested to see which batch of bacteria had labeled material. They discovered that the only bacteria with radioactive material were the ones that had been infected using viruses labeled with phosphorus--basically, DNA, not protein, was being used to pass on genetic material from virus to bacterium. Here is a diagram that does a way better job illustrating what I'm trying to explain:
The main reason why this experiment is extremely cool is that, despite the incredible importance of the findings, it is very simple and straightforward. A lot of the most revolutionary discoveries in science have been made with very simple but elegant experiments. Also, this was one of the first important biology papers coauthored by a woman (I think), so that's pretty neat too.
I have to confess that the main reason why I decided to post this is because I love how, after trying all sorts of high-tech, lab-ey ways to separate the viruses from the bacteria, Hershey and Chase settled on a plain kitchen blender...oh yeah.
For the experiment:
Independent functions of viral protein and nucleic acid in growth of bacteriophage (Hershey and Chase, 1952). [pdf]
Two more simple but very cool and important molecular biology papers:
A Structure for Deoxyribose Nucleic Acid (Watson and Crick, 1953). [pdf]
The replication of DNA in Escherichia coli (Meselson and Stahl, 1958). [pdf]
[Diagram of experiment taken completely without permission from The Pauling Blog.]