Meselson and Stahl carried out centrifugation in CsCl density gradient to separate

Meselson and Stahl carried out centrifugation in CsCl density gradient to separate the normal DNA from ¹⁵N-DNA. Meselson- Stahl experiment showed the semiconservative nature of DNA replication. E.coli growing in presence of ammonium chloride with heavy isotope of nitrogen (¹⁵ N) was transferred to ¹⁴N normal isotope containing medium. One distinct band of ¹⁵N-¹⁴N was obtained after 20 mins. 2nd generation have half ¹⁵N-¹⁴N and other ¹⁴N-¹⁴N DNA. In this manner after 80 mins large fraction of extracted DNA is ¹⁴N-¹⁴N.