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KCET · BIOLOGY · STD 12 - 5. Molecular Basis of Inheritance

E.coli bacteria grew in \({ }^{15} NH _4 Cl\) medium for several generations are allowed to grow in \({ }^{14} NH _4 Cl\) medium. After 2 generations, the bacteria are isolated from the result of the density gradient of DNA is

  1. A only hybrid DNA
  2. B both hybrid and heavy DNA
  3. C both heavy and light DNA
  4. D both hybrid and light DNA
Verified Solution

Answer & Solution

Correct Answer

(D) both hybrid and light DNA

Step-by-step Solution

Detailed explanation

(D) both hybrid and light DNA,
The DNA that was extracted from the culture one generation after transfer from 15N to 14N medium [that is after 20 minutes; E. coli divides in 20 minutes] had a hybrid or intermediate density. DNA extracted from the culture after another generation [that is after 40 minutes, II generation] was composed of equal amounts of this hybrid DNA and of 'light' DNA.