Explain the experiment of Aveny to show DNA acts as genetic material.

Explanation

In 1928 Griffith working on the pathogenicity of streptococcus pneumoniae discovered a process called transformotion. This bacterium is responsible for a form of pneumonia, killing mice. There are two strains of bacteria - smooth strain (S) with a gelatinous coat and a 'rough strain (R) without the gelatinous coat. Smooth strain bacteria are virulent type and kill the mice while rough strain bacteria are avirulent type and do not kill the mice. If live.rough strain bacteria (R) are injected the mouse does not die. When live smooth bacteria are injected the mouse dies. But if heat killed smooth bacteria (S) are injected, the mouse does not die. If a mixture of heat killed smooth bacteria (S) and live rough bacteria (R) is injected into the mice it dies. Some property of heat killed smooth bacteria had transformed R bacterium to become virulent types. This activity was called transfon principle by Griffith.
In 1944. Avery. MacLeod and Mc Carty extended Griffith's experiment to identify the transforming principle. They mixed "R" strain with DNA extracted from 'S' strain of bacteria. When the enzyme (DNAse) which digests or breaks down DNA was added to this mixtures, there was no transformation of R to S type. But when the enzyme proteases that digest proteins wax added to the medium the transformation of R to Sope was not prevented. This confirmed that the transforming principle was DNA.