Here's why:
* Duplication: During the S phase of the cell cycle, each chromosome replicates itself. This means that each chromosome now consists of two identical copies, called sister chromatids.
* Joined: The sister chromatids are held together at a region called the centromere.
* Mitosis: Mitosis is the process where the cell divides to produce two identical daughter cells. The sister chromatids separate during mitosis, ensuring that each daughter cell receives a complete set of chromosomes.
Therefore, at the start of mitosis, each chromosome has two chromatids, representing the duplicated copies of the original chromosome.
