Final answer:
The centromere is the region of a chromosome where two sister chromatids are joined together, and it is essential for the correct segregation of chromosomes during cell division.
Step-by-step explanation:
The region of a chromosome where two sister chromatids are most closely attached to each other is known as the centromere. During DNA replication in the S phase of interphase, chromosomes are replicated to form two identical strands called sister chromatids, which are joined together at the centromere. The centromeric region is very condensed and appears as a constricted area in the chromosome. The centromere contains proteins called kinetochores which are essential for the attachment of the mitotic spindle fibers during mitosis, thereby enabling the sister chromatids to separate and move to opposite poles of the cell.