Question

Which one of the following will be the ratio of heavy, intermediate and light bands in Meselson and Stahl’s experiment after two generations if DNA replication were conservative?

• A. 0 : 2 : 2
• B. 1 : 0 : 3
• C. 2 : 2 : 0
• D. 2 : 0 : 2

Answer 1

Answer: (D)

The Meselson and Stahl's experiment showed that DNA in replicated by semi-conservative mechanism. In conservative replication, on daughter duplex consist of two newly synthesised strand and parental start is conserved. Parental DNA grown is ${}^{15}N$ medium (heavy isotope of nitrogen) when centrifuged in first and second generation produces only light and heavy band because parental DNA contains ${}^{15}N$ in DNA and newly synthesised contain ${}^{14}N$ in bases. No intermediate density band is formed. Intermediate band is formed in semi-conservative and dispersive replication, where one DNA strand contains ${}^{15}N$ and other strand contains ${}^{14}N$.