Final answer:
Each chromosome has a centromere, which is a constricted point where special repeated DNA sequences bind proteins, such as the kinetochore, and is essential during cell division.
Step-by-step explanation:
Each chromosome has a centromere, a point of constriction containing certain repeated DNA sequences that bind specific proteins. The centromere is crucial for chromosome alignment and segregation during cell division as it is where the kinetochores form and where the spindle fibers attach during mitosis. During the S phase of interphase, chromosomes are duplicated, and each consists of two identical sister chromatids joined at the centromere. The kinetochore is a complex of proteins associated with the centromere that connects chromosomes to spindle microtubules. The tightly compacted structure of a chromosome is visible under a microscope, with the centromeric region appearing as a constricted area due to its high level of condensation.