Discussion
Frederick Griffith used smooth (S) and rough (R) strains of Streptococcus pneumoniae in his classical experiment that showed DNA might be the genetic element. Which ONE of the following observations gave the clue for this discovery?
Answer: A
The clue was that the R strain became S strain when mixed with heat killed S strain.
In 1928 Griffith injected mice with live non-virulent rough (R) pneumococci together with heat-killed virulent smooth (S) cells. Neither alone killed the mice, but the mixture did, and live S bacteria were recovered. Something from the dead S cells had permanently transformed the R cells; Avery, MacLeod and McCarty later showed the 'transforming principle' was DNA.
R remaining R would show nothing. S becoming R with killed R cells was not the observation, and mixing R with live S cells proves nothing, because live S bacteria are already present.
Post your comment
Please log in or register to post a comment.
Examination Categories
- SSC Exams
- Banking Exams
- Teaching Exams
- Civil Services Exams
- Railways Exams
- Engineering Recruitment Exams
- Defence Exams
- State Government Exams
- Police Exams
- Insurance Exams
- Nursing Exams
- Other Government Exams
- NRA CET
- PG Entrance Exams
- Campus Placement
- MBA Entrance Exams
- CUET and UG Entrance
- Judiciary Exams
- Regulatory Body Exams
- Software Development