To qualify as the genetic material, DNA has to fulfil two key requirements:
1) Genotype function or Replication: The genetic material must have the capability to store genetic information, and transmit this information faithfully from parents to offspring, generation after generation. This indicates that the genetic material should have the ability to replicate itself and make its copies.
2) Phenotype function or Gene Expression: The genetic material must control the development of phenotype of the organism. It means that it should control the growth and differentiation of the organism from the single-celled zygote to the mature adult.
There are three landmark experiments, which showed that DNA is the genetic material.
1) Griffith’s Experiment (1928)
2) Avery, MacLeod and McCraty’s Experiment (1944): They showed that if highly purified DNA from Type IIIS pneumococci was present with TypeIIR pneumococci, some of the pneumococci were transformed to Type IIIS.
3) Hershey-Chase Experiment (1952): The basis for the experiment: DNA contains phosphorus but no sulfur; whereas proteins contain sulfur but no phosphorus. The experiment is also referred to as the Waring blender experiment.