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Molecular Basis of Inheritance — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYMolecular Basis of Inheritance4 Marks
Question
Study the flow chart given below and answer the questions that follow:
  1. S strain into mice mice die.
  2. R strain into mice → mice live.
  3. Heat killed S strain + live R strain into mice → A
  4. Heat killed S strain + DNase + live R strain → into mice B
  1. Name the organism and differentiate between its two strains, R and S, respectively.
  2. Write the results A and B obtained in steps (e) and (d), respectively.
  3. Name the Scientist who performed the steps (a), (b) and (c).
  4. Write the specific conclusion drawn from the step (d).
✓

Answer

  1. Streptococcus pneumoniae:
  1. R-cells are those cells that form rough colonies, without a capsule and are non-virulent, i.e., they did not cause pneumonia.
  2. S-cells are those cells that form smooth colonies, protected by a capsule and are virulent, i.e., they caused the disease, pneumonia.
  3. He showed that DNA is the transforming principle.
  1. A. Mice died of pneumonia. B. Mice lived and did not suffer from pneumonia.
  2. Frederick Griffith performed the steps (a), (b) and (c).
  3. This indicates that DNA is the transforming principle.

When DNase is added to the medium, the DNA of the heat-killed cells gets digested and is unable to carry out the transformation.

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