A cell containing a single chromosome is placed in a medium containing radioactive phosphate so that any new DNA strands formed by DNA replication will be radioactive. The cell replicates its DNA and divides. Then the daughter cells (still in the radioactive medium) replicate their DNA and divide, and a total of four cells are present. Sketch the DNA molecules in all four cells, showing a normal (nonradioactive) DNA strand as a solid line and a radioactive DNA strand as a dashed line.

Verified step by step guidance

1. Step 1: Understand the initial condition of the cell. The cell starts with one chromosome, which consists of two DNA strands intertwined in a double helix. Since the cell is placed in a medium with radioactive phosphate before any replication occurs, only the new strands synthesized will incorporate the radioactive material.
2. Step 2: Visualize the first round of DNA replication. Each strand of the original DNA serves as a template for a new strand. Since the new strands are synthesized in the presence of radioactive phosphate, they will be radioactive. Represent the original DNA strand as a solid line and the new, radioactive strand as a dashed line. After replication, each chromosome will consist of one solid line and one dashed line.
3. Step 3: Consider the cell division that follows the first DNA replication. The cell divides into two daughter cells, each inheriting one chromosome from the original cell. Each of these chromosomes will have one solid line (original non-radioactive strand) and one dashed line (new radioactive strand).
4. Step 4: Account for the second round of DNA replication in the daughter cells, which are still in the radioactive medium. Each strand (solid and dashed) in both daughter cells now acts as a template for a new strand. The new strands synthesized will again be radioactive (dashed lines). After this replication, each chromosome in the daughter cells will consist of one solid line paired with one dashed line and one dashed line paired with another dashed line.
5. Step 5: Sketch the final outcome after the second cell division, resulting in four cells. Each of these four cells will contain chromosomes as described in step 4. Two cells will have chromosomes with one solid line and one dashed line, and two cells will have chromosomes with both strands as dashed lines, indicating they are fully radioactive.