Question

Transformation was discovered by?

Answer 1

Hint:Nucleic acid is of two types in all living systems i.e., deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA is genetic material in all organisms except some viruses. RNA is genetic material in riboviruses. DNA is a substance that controls the inheritance of traits from one generation to the next.

Complete answer:
DNA is a long polymer of deoxyribonucleotides. It is an acidic substance found inside the nucleus of a cell, which was first identified by Friedrich Meischer in 1869. He named it "Nuclein". Altmann found these substances to be acidic in nature, hence he named them macromolecules. The length of DNA is typically defined as the number of nucleotides or a pair of nucleotides mentioned as base pairs (bp) present in it. This is one of the characteristic features of an organism. For example E. coli has 4.6 x 10^6 bp and the human genome has 3.3 x 10^9 bp.
The basic unit of DNA has three components- a nitrogenous base, a pentose sugar and a phosphate group.
Even though the discovery of nuclein by Meischer and the proposition for principle of the inheritance by Mendel were almost the same at the same time, but that the DNA acts as a genetic material took long to be discovered and proven. One of such experiments to prove the inheritance property of DNA was The Transforming Principle.
The Transforming experiments were conducted by Frederick Griffith in 1928. He performed a series of experiments by selecting two strains of bacteria Streptococcus pneumoniae, namely, S-III and R-II.
The S-III strain is smooth and capsulated and produces smooth shiny colonies in the culture plate. These are virulent and cause pneumonia.
R-II strains are rough and non-capsulated types with no mucous coat. These are non-virulent and don't cause pneumonia.
By his experiments, Griffith concluded that the R-strain bacteria had somehow been transformed by the heat-killed S-strain bacteria. This occurred perhaps thanks to absorption of some transforming principle or substance by rough-type bacteria. It had enabled the R-strain to synthesize a smooth polysaccharide coat and become virulent. This must be due to the transfer of genetic material. But the biochemical nature of genetic material wasn't defined from his experiments.

Note:
Biochemical characterization of the Transforming Principle was discovered by Avery, Macleod, and McCarty in an in-vitro experiment. They proved that this substance is DNA. Before they proved it, the genetic material was thought to be protein. They purified biochemical proteins, DNA and RNA from the heat-killed S-cells to see which ones could transform live R-cells into S-cells.