What changes into a sister chromatid?

A sister chromatid is formed during the S phase of the cell cycle when a chromosome is replicated. Each chromosome, which consists of a single DNA molecule, duplicates to create two identical copies, known as sister chromatids, connected at a region called the centromere. These chromatids remain linked until the cell divides during mitosis or meiOSis, ensuring that each daughter cell receives an identical set of chromosomes.