Question

After crossing over has already occurred, the ________ assembles near the centromere and allows microtubules to attach so that centromeres can be pulled to opposite poles

Answer 1

Crossing over occurs in the pachytene stage of prophase I of meosis I (reductional division). After crossing over, the homologous chromosomes remain attached at a point called chiasmata in diplotene stage. In the diakinesis stage, the nuclear membrane disintegrates, aligning the homologous chromosomes to the centre of the cell, with the homologous chromosomes facing one another. Each chromosome has four sister chromatids and a centromere. Kinetochore assembles itself around the centromere, thus providing a surface for the microtubules to attach to to the chromosome through the kinetochore. Centromere's role is to provide a base for the assembling of the kinetochore proteins. Around 80 proteins constitute the kinetochore. The microtubules attach to the kinetochore side wise, pulling the chromosome via centromere to the opposite pole.

Hence, the answer is " After crossing over has already occurred, the kinetochore assembles near the centromere and allows microtubules to attach so that the centromere can be pulled to opposite poles".