Detection of semiconservative replication of E. coli DNA by density-gradient centrifugation. The position of a band of DNA depends on its content of ¹⁴N and ¹⁵N. After 1.0 generation, all of the DNA molecules were hybrids containing equal amounts of ¹⁴N and ¹⁵N.

[Data from M. Meselson and F. W. Stahl. Proc. Natl. Acad. Sci. U. S. A. 44:671–682, 1958.]