Question

In microbial genetics which one is referred to as “Griffith effect”?
(a)Conjugation
(b)Transduction
(c)Transformation
(d)Sex-duction

Answer 1

Hint: Discovery of DNA as genetic material was proven by the experiment conducted by Frederick Griffith in 1928 which stabilized the nature of genetic material. He thought that there is a transfer of genes that was proved by his experiment.

Complete answer:
Even though after the discovery of nuclei by Meischer and the proposition for the principle of inheritance by Mendel were done, the DNA acts as a genetic material that was discovered after a long time.
The transforming principle: The transformation experiment, conducted by Frederick Griffith in 1928, are of great evidence in establishing the nature of genetic material. He performed a series of experiments by selecting two strains of bacterium Streptococcus pneumoniae (also called Pneumococcus) namely, S-III and R-II.

Additional Information: -S-III strain/smooth (capsulated type) have a mucus coating and produce smooth shiny colonies on a culture plate. These are virulent and cause pneumonia.
-R-II strain/rough (non-capsulated type) have no mucus coat and produce rough colonies. These are non-virulent and do not cause pneumonia.
-He observed that heat-killed S-III strain bacteria injected into mice did not kill them. But when he injected a mixture of heat-killed S and live R bacteria, the mice died.
-He concluded that R strain bacteria had somehow been transformed by the heat-killed S strain bacteria. This occurred due to the absorption of transforming principle or substance by R type bacteria from S type bacteria.
-Thus, he concluded that this is due to the transfer of genetic material and named this principle as transforming principle.
So, the answer is, ‘Transformation’.

Note: -Griffith was able to kill bacteria by just heating it and then injected this heat-killed bacteria with live R bacteria.
-He recovered living S bacteria from the dead mice which meant that the virulent property of S bacteria which was heat-killed got transferred into non-virulent R bacteria.
-DNA as genetic material was not discovered by Griffith, he just named it as a transforming substance.
-DNA was proved as a genetic material by Avery, Macleod, and McCarty (1944) who repeated the experiment in vitro to identify the biochemical nature of transforming substances.