Question

Meselson and stahl cultured
e. coli for several generations in a medium with a heavy isotope of nitrogen, 15n. they transferred the bacteria to a medium with a light isotope of nitrogen, 14 n. after two rounds of dna replication, half the dna molecules were light (both strands had 14n and half were hybrids (15n-14n. what did the researchers conclude from these results?

Answer 1

Meselson and Stahl concluded that DNA replication is semiconservative. 

The DNA replication is identified as semi conservative because the two copies it produces each contains one original strand and one new strand.  14n is the original strand while the hybrid represent the new strand.