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Molecular Basis of Inheritance — BIOLOGY STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 ScienceBIOLOGYMolecular Basis of Inheritance3 Marks
Question
What is ‘semi-conservative’ DNA replication? How was it experimentally proved and by whom?
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Answer

After the completion of replication (of the DNA molecule into two)) each DNA molecule will have one parental strand and newly synthesised strand.

 Meselson and Stahl

  1. E.coli grown in medium containing 15NH4CL (15N - heavy Nitrogen) for many generations to ensure that all DNA in the bacteria were heavy,
  2. Heavy E.coli transferred to a medium with normal 14NH4CL,(after 20 minutes) DNA of generation I extracted to measure their densities, they were of intermediate density,
  3. After 40 minutes DNA of II generation were extracted and tested for their densities, they were of equal amounts of (hybrid) intermediate DNA, and light DNA/14NH4Cl.

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