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

E.coli fully labelled with \({ }^{15} N\) is allowed to grow in \({ }^{14} N\) medium. The two strands of DNA molecule of the first generation bacteria have

A same density and resemble with their parent DNA.
B same density but do not resemble with their parent DNA.
C different density but do not resemble with their parent DNA.
D different density but resemble with their parent DNA

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Answer & Solution

Correct Answer

(C) different density but do not resemble with their parent DNA.

Step-by-step Solution

Detailed explanation

(C) different density but do not resemble with their parent DNA.,
In the experiment of Meselson and Stahl's heavy ( \({ }^{15} N\) ) and light ( \({ }^{14} N\) ) isotopes of nitrogen are used to distinguish between parental and newly synthesized DNA strands.

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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