Final answer:
Before a cell divides, it must replicate its DNA to ensure each daughter cell receives an identical genetic copy. Post-replication, DNA condenses into chromosomes for accurate distribution during mitosis. option a is correct.
Step-by-step explanation:
Before a cell can divide, it must first replicate its DNA during the synthesis phase, or S phase, of the cell cycle. This is a critical step to ensure that each daughter cell receives an exact copy of the organism's genome. DNA replication involves unwinding the DNA and using the original strands as templates for building complementary strands, creating two identical DNA molecules, each with one original strand and one new strand.
Once DNA replication is complete, the DNA coils tightly and condenses to form chromosomes. This condensation into chromosomes occurs so that during mitosis, the replicated genetic material can be sorted and separated accurately to each daughter cell.
After DNA has replicated, one copy goes to each new cell, ensuring genetic continuity. It is only after DNA has replicated that it condenses into the X-shaped chromosomes with sister chromatids, joined at the centromere. During prophase, these chromosomes become visible under a microscope as they attach to spindle fibers that will divide them during cell division.