“Transforming Principle” was given by:

The correct answer is Option (2) → Frederick Griffith

Option (1) Maclyn McCarty — Incorrect. McCarty, with Avery and MacLeod, later found what the transforming principle is: DNA. They did not name it.

Option (2) Frederick Griffith — Correct. In 1928 Griffith worked with Streptococcus pneumoniae in mice. He found that something from heat-killed S strain bacteria changed live R strain bacteria into the virulent S form, and called it the transforming principle.

Option (3) Alfred Hershey — Incorrect. Hershey, with Chase, used bacteriophages to show that DNA is the genetic material.

Option (4) Watson and Crick — Incorrect. Watson and Crick proposed the double helix model of DNA in 1953.

NCERT Extract:
The Search for Genetic Material – “… Griffith was able to kill bacteria by heating them. He observed that heat-killed S strain bacteria injected into mice did not kill them. 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 synthesise a smooth polysaccharide coat and become virulent.”