It was experimented by Fredrick Griffith he use two strain (rough and smooth) of bacteria which injected in the mice and by the process of transformation it was concluded that "DNA is the genetic material ".

The Pneumococcus experiment, conducted in 1928 by Frederick Griffith, was a groundbreaking study that provided evidence for the role of DNA as the genetic material. This experiment involved the transformation of non-virulent bacteria into virulent bacteria through the transfer of genetic material.

Background:
Before the Pneumococcus experiment, it was not known which molecule carried the genetic information in cells. The two main candidates were DNA and proteins. DNA was considered a candidate because it exhibited chemical properties that suggested it could store and transmit genetic information. On the other hand, proteins were thought to be more complex and diverse, making them potential candidates for carrying genetic information.

Experimental Setup:
Griffith used two strains of the bacterium Streptococcus pneumoniae: a non-virulent strain (R strain) and a virulent strain (S strain). The R strain lacked a protective capsule, making it harmless, while the S strain had a capsule and was capable of causing disease.

Griffith conducted four different experiments:

1. Control Experiment: He injected mice with the non-virulent R strain bacteria, and the mice remained healthy.

2. Virulent S Strain Experiment: He injected mice with the virulent S strain bacteria, and the mice died due to pneumonia.

3. Heat-Killed S Strain Experiment: He killed the virulent S strain bacteria by heat treatment and injected the heat-killed bacteria into mice. The mice remained healthy.

4. Mixture of Heat-Killed S Strain and Live R Strain Experiment: He mixed the heat-killed S strain bacteria with the live R strain bacteria and injected this mixture into mice.

Results:
Surprisingly, the mice injected with the mixture of heat-killed S strain and live R strain bacteria died. Upon examination, Griffith found live virulent S strain bacteria in the dead mice. This outcome indicated that the live R strain bacteria had been transformed into the virulent S strain.

Conclusion:
From these results, Griffith concluded that the genetic material responsible for the transformation was transferred from the heat-killed S strain bacteria to the live R strain bacteria. This transfer of genetic material resulted in the live R strain bacteria acquiring the ability to produce a capsule and becoming virulent.

This experiment provided the first evidence that DNA can carry and transmit genetic information. It demonstrated that the DNA from the heat-killed bacteria was taken up by the live bacteria and incorporated into their own genetic material, leading to a change in their phenotype. This finding laid the foundation for further research into the structure and function of DNA and ultimately led to the confirmation that DNA is indeed the genetic material in cells.

In summary, the Pneumococcus experiment proved that DNA is the genetic material by showing that the transfer of DNA from one bacterium to another could change the phenotype of the recipient bacterium.