During which stage do spindle fibers attach to kinetochores on chromosomes?

During which stage do spindle fibers attach to kinetochores on chromosomes?

• A. Prophase
• B. Metaphase
• C. Anaphase
• D. Prometaphase

Answer: (D)

Spindle fibers attach to kinetochores when the chromosomes become accessible to the spindle apparatus after the nuclear envelope breaks down. Kinetochores are protein structures located at the centromeres of chromosomes, and the microtubules of the spindle attach to these sites to exert forces that move chromosomes toward the center of the cell. This attachment happens during prometaphase, right after chromatin condenses and the nuclear envelope dissolves, allowing microtubules to interact with kinetochores. By metaphase, those attachments are established and chromosomes line up at the metaphase plate, while in prophase the spindle forms but the envelope is still intact, and in anaphase the sister chromatids are pulled apart once cohesins are cleaved. So the stage when spindle fibers first attach to kinetochores is prometaphase.

Spindle fibers attach to kinetochores when the chromosomes become accessible to the spindle apparatus after the nuclear envelope breaks down. Kinetochores are protein structures located at the centromeres of chromosomes, and the microtubules of the spindle attach to these sites to exert forces that move chromosomes toward the center of the cell. This attachment happens during prometaphase, right after chromatin condenses and the nuclear envelope dissolves, allowing microtubules to interact with kinetochores. By metaphase, those attachments are established and chromosomes line up at the metaphase plate, while in prophase the spindle forms but the envelope is still intact, and in anaphase the sister chromatids are pulled apart once cohesins are cleaved. So the stage when spindle fibers first attach to kinetochores is prometaphase.