Final answer:
Spindle fibers connect at the centromere of duplicated chromosomes, specifically to a structure called the kinetochore, during metaphase in cell division processes like mitosis and meiosis.
Step-by-step explanation:
Spindle fibers connect to duplicated chromosomes at the centromere of each pair of sister chromatids. This occurs during the metaphase of both mitosis and meiosis.In the process of cell division, either mitosis or meiosis, duplicated chromosomes become highly condensed and visible as sister chromatids. These chromatids are connected through a specialized structure known as the centromere. During the metaphase stage, spindle fibers, which are composed of microtubules, attach to the centromere at a region called the kinetochore. Kinetochore microtubules emerge from the spindle apparatus, which includes centrioles or microtubule-organizing centers (MTOCs) at the cell poles.
These microtubules bind to the kinetochore, ensuring that each sister chromatid is oriented correctly and prepares them for segregation into different daughter cells when the cell enters anaphase and eventually divides. Some spindle fibers are not involved in chromosome attachment; these include polar microtubules, which help elongate the cell, and astral microtubules, which are involved in spindle orientation and mitosis regulation. It is essential for the correct number of microtubules to bind each kinetochore to ensure genetic material is equally divided, leading to proper cell division.