The important experiments in the history of genetics are all MCAT favorites, appearing in one form or another over the years, often as starting points for passages. You definitely need to be aware in rough outline, at least, of the work of Miescher Griffith - Avery, MacLeod, & McCarty and Hershey and Chase. These experiments together firmly established that genes are composed of DNA.

Watson and Cricks discovery of the structure of DNA subsequently led to the understanding of how genes carry hereditary information. The fundamental understanding, the central dogma, is that a gene is a section of DNA that codes for a specific mRNA, which in turn contains the code for a polypeptide. A gene may also code for a structural RNA molecule. This is the 'central dogma' of molecular biology, in other words, the understanding in basic outline of the processes of transcription and translation.