Final answer:
Sister chromatids are held together by the centromere, which is essential for chromosome segregation during cell division.
Step-by-step explanation:
The sister chromatids are held together by the centromere. Chromosomes are duplicated during interphase, and it is at the centromere that the resulting sister chromatids are bonded. This connection is crucial for the correct segregation of chromosomes during cell division. The centrosomes are also duplicated during this phase, but they play a different role in the process of cell division, particularly in forming the spindle apparatus, which is essential for the movement of chromosomes during mitosis and meiosis.