Describe the different experiments which prove that $DNA$ is a genetic material.

(A) Even though the discovery of nuclein by Meischer and the proposition for principles of inheritance by Mendel were almost at the same time,the fact that $DNA$ acts as a genetic material took a long time to be discovered and proven.
By $1926$,the quest to determine the mechanism for genetic inheritance had reached the molecular level.
Previous discoveries by Gregor Mendel,Walter Sutton,Thomas Hunt Morgan,and numerous other scientists had narrowed the search to the chromosomes located in the nucleus of most cells.
$1$. Transforming Principle: In $1928$,Frederick Griffith,in a series of experiments with $Streptococcus$ $pneumoniae$ (bacterium responsible for pneumonia),witnessed a miraculous transformation in the bacteria.
During the course of his experiment,a living organism (bacteria) changed in physical form. When $Streptococcus$ $pneumoniae$ bacteria are grown on a culture plate,some produce smooth shiny colonies $(S)$ while others produce rough colonies $(R)$.
This is because the $S$ strain bacteria have a mucous (polysaccharide) coat,while the $R$ strain does not.
Mice infected with the $S$ strain (virulent) die from pneumonia infection,but mice infected with the $R$ strain do not develop pneumonia.
$S$ strain $\rightarrow$ Inject into mice $\rightarrow$ mice die
$R$ strain $\rightarrow$ Inject into mice $\rightarrow$ mice live
Griffith was able to kill bacteria by heating them.
He observed that heat-killed $S$ strain bacteria injected into mice did not kill them.
$S$ strain (heat-killed) $\rightarrow$ Inject into mice $\rightarrow$ mice live
$S$ strain (heat-killed) $+$ $R$ strain (live) $\rightarrow$ Inject into mice $\rightarrow$ mice die
When he injected a mixture of heat-killed $S$ and live $R$ bacteria,the mice died. Moreover,he recovered living $S$ bacteria from the dead mice.
He concluded that the $R$ strain bacteria had somehow been transformed by the heat-killed $S$ strain bacteria. Some 'transforming principle' transferred from the heat-killed $S$ strain had enabled the $R$ strain to synthesize a smooth polysaccharide coat and become virulent. This must be due to the transfer of the genetic material. However,the biochemical nature of the genetic material was not defined from his experiments.