E. coil cells grown on 15 N medium are transferred to 14 N medium and allowed to grow for two generations. DNA extracted from these cells is ultracentrifuged in a cesium chloride density gradient. What density distribution of DNA would you expect in this experiment? (a) What did Meselson and Stahl observe when
(i) They cultured E. coli in a medium containing
15
NH
4

Cl for a few generations and centrifuged the content.
(ii) They transferred one such bacterium to the normal medium of NH
4

Cl and cultured for two generations.

The hershey and chase experiments involved the preparation of two different types of radioactively labeled phage. which of the following best explains why two preparations were required? a. the bacteriophage used in the experiments was a t2 phage. b. it was necessary that each of the two phage components, dna and protein, be identifiable upon recovery at the end of the experiment. c. each scientist had his own method for labeling phage, so each conducted the same experiment using a different isotope. d. establishing the identity of the genetic material required observation of two phage generations.