Final answer:
The three classic experiments that established DNA as the hereditary molecule include Frederick Griffith's transformation experiment in 1928, the Avery-MacLeod-McCarty experiment in 1944, and the Hershey-Chase experiment in 1952, together with Chargaff's base pairing rules.
Step-by-step explanation:
Key Historical Experiments in DNA Research
The identification of DNA as the genetic material was a major milestone in biology, achieved through several pivotal experiments. These experiments included the works of Frederick Griffith, Oswald Avery, Colin McLeod, and Maclyn McCarty, and Hershey and Chase.
Frederick Griffith's Experiment
In 1928, Frederick Griffith demonstrated that a substance from dead encapsulated bacteria could transform live nonencapsulated bacteria into virulent forms. This was the first indication that a molecule could transfer genetic material, but the nature of the molecule was not yet known.
Avery-MacLeod-McCarty Experiment
In 1944, the scientists Oswald Avery, Colin McLeod, and Maclyn McCarty identified DNA as the transforming principle discovered by Griffith. This was compelling evidence that DNA was responsible for heredity, but still not universally accepted due to beliefs about the complexity needed for genetic information.
Hershey-Chase Experiment
A clear confirmation came in 1952 with the Hershey and Chase experiment, which used radioactive labeling to demonstrate that DNA from bacteriophages, not proteins, entered bacteria and directed the production of progeny viruses, proving that DNA is the hereditary material.
These historic experiments, coupled with Chargaff's rules of base pairing, where adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G), provided the essential insights leading to the widely accepted conclusion that DNA is the molecule responsible for heredity.