NEET Botany Molecular Basis of Inheritance Questions Solved


State the aim and describe Messelson and Stahl's experiment.

Messelon and Stahl's experiment : 

(i) They grew E.coli in a medium containing N15H4Cl as the only nitrogen source for many generations. The result was that N15 was incorporated into newly synthesised DNA. 

(ii) The heavy DNA molecule could be distinguished from the normal DNA by centrifugation in a cesium chloride density gradient. 

    (Separation of DNA by centrifugation)

     Messelson's and Stahl's experiment) 

(iii) They transferred the cells into a medium with normal 14NH4Cl and took samples at various definite time intervals as the cells multiplied, and extracted the DNA that remained as doubled-stranded helicals.

(iv) Thus, the DNA that was extracted from the culture one generation after the transfer from 15N

to 14N medium (i.e., E.coli divides in 20 minutes) had hybrid or intermediate density. 

(v) DNA extracted from the culture after another generation (that is after 40 minutes, II generation) was composed of equal amounts of the hybrid DNA and of light DNA.                                    (5)

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