Before the next mitosis cycle can start, a chromosome must replicate itself. Here's why:

* Mitosis is about creating two identical daughter cells. Each daughter cell needs a complete set of chromosomes.

* Chromosomes are the carriers of genetic information. If chromosomes aren't duplicated, the daughter cells will be missing half of their genetic material.

The process of chromosome replication happens during the S phase of the cell cycle, which occurs between G1 and G2 phases.

Here's a simplified breakdown:

1. S Phase: The DNA in each chromosome is copied, creating two identical sister chromatids. The sister chromatids remain attached at the centromere.

2. G2 Phase: The cell grows and prepares for mitosis.

3. Mitosis: The sister chromatids separate, and each daughter cell receives one complete set of chromosomes.

This replication process ensures that each new cell has the same genetic information as the parent cell.