Botany

Bacteria were grown in medium for many generations. This step allowed the bacteria to incorporate the heavier isotope ( ) into all of their DNA. After growing in the medium for several generations, the bacteria contained only -labeled DNA. Bacteria were then transferred to an medium and sampled every 20 minutes. In this step, the bacteria were placed in a medium containing the lighter nitrogen isotope ( ). Sampling at regular intervals allowed the researchers to track how DNA was replicated in the new medium. After one round of replication, the bacteria's DNA was hybrid-one strand from the heavy DNA and one newly synthesized light strand containing . After several rounds of replication, the bacteria had either completely labeled DNA (newly synthesized) or hybrid DNA, further supporting the semi-conservative model of DNA replication.

──────────────────────────────────────────────────────────────────────────────────────────