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Molecular Basis of Inheritance — BIOLOGY STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceBIOLOGYMolecular Basis of Inheritance3 Marks
Question
DNA separated from one cell, when introduced into another cell is able to bestow some of the properties of former to the latter. What is this change called in technical terms? Describe the experimental evidences which led to the discovery of the above phenomenon.
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Answer

This change is called transformation.Transforming Principle:
  • Frederick Griffith (1928) conducted experiments with Streptococcus pneumoniae (bacterium causing pneumonia).
  • He observed two strains of this bacterium-one forming smooth shiny colonies (S-type) with capsule, while other forming rough colonies (R-type) without capsule.
  • When live S-type cells were injected into mice, they died due to pneumonia.
  • When live R-type cells were injected into mice, they survived.
  • When heat-killed S-type cells were injected into mice, they survived and there were no symptoms of pnuemonia.
  • When heat-killed S-type cells were mixed with live R-type cells and injected into mice, they died due to unexpected symptoms of pneumonia and live S-type cells were obtained from mice.
  • He concluded that heat-killed S-type bacteria caused a transformation of the R-type bacteria into S-type bacteria but he was not able to understand the cause of this bacterial transformation.

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