Question

E. coil cells grown on ${}^{15}\text{N}$ medium are transferred to ${}^{14}\text{N}$ 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. One high and one low density band
• B. One high and one intermediate density band
• C. One low and one intermediate density band
• D. One intermediate density band.

Answer 1

Answer: (C)

The correct option is D One low and one intermediate density band
E. coil cells grown on 15N15N medium are transferred to 14N14N medium and allowed to grow for two generations. DNA extracted from these cells is ultracentrifuged in a cesium chloride density gradient. Since DNA has a semiconservative nature, the products or genomes obtained after two generations will have both the isotopes of N. So, the density distribution will show One low and one intermediate density band.

So, the correct option is 'One low and one intermediate density band'.