Question

The transforming principle in Griffith's experiment was detected

• A. When live S-strain of S. pneumoniae was injected into mice.
• B. When live R-strain of S. pneumoniae was injected into mice.
• C. When heat killed R-strain of S. pneumoniae was injected into mice.
• D. When mixture of heat killed S-strain and live R-strain of S. pneumoniae was injected into mice.

Answer 1

Answer: (D)

Griffith in the search for genetic material conducted experiments with the pneumonia causing bacteria Streptococcus pneumoniae. When these bacteria are grown on culture some produced the smooth colonies (S) and other produced rough colonies (R). The mice infected with S strain dies and those with R did not. After heat killing the bacteria he observed that these heat killed S strain did not cause any disease. But when he injected the mixture of heat killed S strain and R strain the mice died, and also he could recover living S strain from the dead mice. From this he concluded that there is some transforming principle which helped R starin to become virulent and cause death.