TRANSFORMING PRINCIPLE
Read the following passage carefully and answer the given questions.
When Streptococcus pneumoniae bacteria are grown on a culture plate, some produce smooth shiny colonies while others produce rough colonies. This is because the S strain bacteria have a mucous coat, while R strain does not. Mice infected with the S strain die from pneumonia infection but mice infected with the R strain do not develop pneumonia. Griffith 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. This must be due to the transfer of the genetic material. However, the biochemical nature of genetic material was not defined from his experiments.
Transforming experiment using bacteria and mice were performed by:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Frederick Griffith
In 1928 Frederick Griffith injected mice with Streptococcus pneumoniae. Live S bacteria killed the mice, live R bacteria did not, and heat-killed S bacteria did not. A mixture of heat-killed S and live R bacteria killed the mice. He recovered live S bacteria from the dead mice, so R bacteria had been transformed.
(1) Frederick Griffith — Correct. He did the transformation experiment with bacteria and mice.
(2) Alfred Hershey and Martha Chase — Incorrect. They worked with bacteriophages and radioactive labels, not with mice.
(3) Oswald Avery, Colin MacLeod and Maclyn McCarty — Incorrect. They worked out the chemical nature of Griffith’s transforming principle by purifying biochemicals from the heat-killed S cells. They showed it is DNA.
(4) Friedrich Meischer — Incorrect. He discovered nuclein in the nucleus. He did not do a transformation experiment.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
The Search for Genetic Material – …
