Which of the following structures forms attachments with the chromosomes during pro-metaphase?

During pro-metaphase, the spindle fibers play a crucial role in the attachment to chromosomes. Spindle fibers are part of the mitotic apparatus, which is a collection of structures that orchestrate cell division. Specifically, these fibers extend from the centrosomes at the poles of the cell towards the chromosomes, facilitating their movement and alignment along the metaphase plate.

In this phase, spindle fibers bind to the kinetochores, which are protein structures on the chromosomes. This attachment is essential for the proper segregation of chromosomes into the daughter cells during anaphase. The dynamic nature of the spindle fibers, with their ability to grow and shrink, allows for the necessary tension and orientation needed for the accurate distribution of genetic material.

Other structures, such as the nuclear envelope, dismantle during prophase, allowing the spindle fibers to access the chromosomes. Centrioles, while important in organizing the spindle apparatus during the earlier stages of cell division, do not directly interact with the chromosomes themselves during pro-metaphase. Rather, they serve as a foundation from which the spindle fibers originate. Thus, the mitotic apparatus, particularly the spindle fibers, is the correct structure responsible for chromosome attachment during this critical phase of mitosis.