Grains represent radioactive material within the replicating eye.
-In an experiment, DNA is allowed to replicate in an environment with all necessary enzymes, dATP, dCTP, dGTP, and radioactively labeled dTTP (³H thymidine)for several minutes and then switched to nonradioactive medium. It is then viewed by electron microscopy and autoradiography. The figure above represents the results.
Which of the following is the most likely interpretation?
A) There are two replication forks going in opposite directions.
B) Thymidine is only being added where the DNA strands are furthest apart.
C) Thymidine is only added at the very beginning of replication.
D) Replication proceeds in one direction only.

Question

Grains represent radioactive material within the replicating eye.
-In an experiment, DNA is allowed to replicate in an environment with all necessary enzymes, dATP, dCTP, dGTP, and radioactively labeled dTTP (³H thymidine)for several minutes and then switched to nonradioactive medium. It is then viewed by electron microscopy and autoradiography. The figure above represents the results.
Which of the following is the most likely interpretation?
A) There are two replication forks going in opposite directions. 
B) Thymidine is only being added where the DNA strands are furthest apart. 
C) Thymidine is only added at the very beginning of replication. 
D) Replication proceeds in one direction only.

Quizplus · Accepted Answer

The presence of radioactively labeled thymidine only at specific sections of the DNA, as would be visualized by autoradiography, suggests that replication is occurring at two sites moving away from a common origin, indicating two replication forks going in opposite directions.

Grains Represent Radioactive Material Within the Replicating Eye