Question

Cultured mammalian cells grown in thymidine for many generations were allowed to undergo replication in the presence of bromodeoxyuridine (BrdU), which replaces thymidine in DNA. After two rounds of replication, what would the DNA look like if replication were conservative?

a. All chromatids have one strand that contains BrdU and one strand that does not.
b. All chromatids have two strands that contain BrdU.
c. Half of the chromatids have two strands that contain BrdU and half of the chromatids have 2 strands lacking BrdU. d. Both strands of each chromatid contain mixtures of BrdU and thymidine.
e. 75% of the chromatids have two strands that contain BrdU and 25% of the chromatids have 1 strand lacking BrdU and 1 strand containing BrdU.

Answer 1

The DNA would look like All chromatids have one strand that contains BrdU and one strand that does not if replication were conservative.

Step-by-step explanation:

The correct answer is option a. All chromatids have one strand that contains BrdU and one strand that does not.

In conservative replication, the parental DNA is conserved, and the daughter DNA is newly synthesized. Each of the two parental DNA strands acts as a template for new DNA to be synthesized, resulting in each double-stranded DNA having one parental or 'old' strand and one 'new' strand.

In the given scenario, after two rounds of replication in the presence of BrdU, the DNA would look like the following: all chromatids have one strand that contains BrdU (newly synthesized during replication in the presence of BrdU) and one strand that does not (from the original DNA).