Final answer:
A kinetochore is a protein complex on the centromere of a chromosome that facilitates the attachment of spindle microtubules during cell division. After DNA replication forms sister chromatids, they are bound together by cohesin proteins at the centromere until anaphase.
Step-by-step explanation:
A kinetochore is a protein complex that forms at the centromere of a chromosome during cell division. It serves as the attachment point for spindle microtubules, which are necessary to pull sister chromatids apart during mitosis.
When DNA replicates in the S phase of interphase, it forms a replicated chromosome composed of two identical halves called sister chromatids, which remain connected by cohesin proteins at the centromere until they are separated into individual chromosomes during anaphase.
During late prophase, or prometaphase, microtubules from the mitotic spindle invade the former nuclear area and attach to the kinetochores.
This attachment is crucial for proper chromosome alignment on the metaphase plate and their subsequent segregation into the two new daughter cells. The centromeric region is highly condensed, making it visible under a light microscope as a constricted area.