Question

A DNA molecule in which both strands have radioactive thymidine is allowed to duplicate in an environment containing non-radioactive thymidine. What will be the exact number of DNA molecules that contains the radioactive thymidine after 3 duplications?

• A. One
• B. Two
• C. Four
• D. Eight

Answer 1

The correct option is B Two

A DNA molecule in which, both the strands have radioactive thymidine is allowed to duplicate in an environment containing non-radioactive thymidine. The number of DNA molecules, that contains the radioactive thymidine after three duplications will be two because the mode of DNA replication is semiconservative, which leads to the production of two DNA molecules with radioactive thymidine. After the second duplication, the two molecules of DNA out of four contains radioactive thymine strand while the third duplication leads to the formation of two molecules of DNA with radioactive thymine strand out of eight.

So, the correct answer is option B.