Final answer:
The substance initially believed to be the genetic material in the 1940s was proteins. It wasn't until the Hershey and Chase experiments that DNA was confirmed as the genetic material, as they showed DNA, not protein, was transferred to bacteria by viruses.
Step-by-step explanation:
In the 1940s, proteins were initially believed to be the genetic material due to their structural complexity and the variety of amino acids they contained. However, this view changed following key experiments by scientists such as Hershey and Chase, who provided confirmatory evidence that DNA was the genetic material, not proteins.
In their famous experiment with bacteriophages, they used radioactive isotopes to differentiate between DNA and protein, finding that DNA was the substance transferred to bacteria, thus it must be the genetic material. The Hershey and Chase experiments are critical in genetics as they marked the definitive proof that DNA was the hereditary substance.
Prior to this, the high variability in proteins due to their 20 different amino acids made proteins a more likely candidate. These experiments helped shift the scientific consensus towards DNA, despite its seemingly simple structure consisting of only four types of nucleotides.