Meselson and Stahlʹs Experiments Involved Growing E

Multiple Choice

Meselson and Stahlʹs experiments involved growing E. coli on a medium containing ¹⁵N heavy nitrogen) which increased the density of the bacterial DNA. Cells were then grown on a medium containing only ¹⁴N. DNA samples were obtained for analysis after one, two and three rounds of replication generations) and centrifuged on a density gradient. The double-helical DNA forms bands in the gradient depending on its density. How many bands did Meselson and Stahl see after two generation of cells were grown on the ¹⁴N medium?

A) One with DNA containing both ¹⁵N and ¹⁴N.
B) Two, one with DNA containing only ¹⁵N and one with DNA containing only ¹⁴N.
C) Two, one with DNA containing both ¹⁵N and ¹⁴N and one with DNA containing only 14_N.
D) Three, one with DNA containing only ¹⁵N, one with DNA containing both ¹⁵N and ¹⁴N and one with DNA containing only ¹⁴N.