Final answer:
During prophase, chromatin condenses into chromosomes, each consisting of two sister chromatids joined at a centromere. These structures become visible under a microscope, setting the stage for cell division. In meiosis, homologous chromosomes pair as tetrads, with sister chromatids visible, and remain connected at chiasmata.
Step-by-step explanation:
During prophase, the initial phase of mitosis, the loosely packed chromatin coils and condenses into more visible structures known as chromosomes.
It is during this stage that each chromosome becomes visible with its identical partner, known as a sister chromatid, attached, thus forming the characteristic X-shape.
The binding at the center of these sister chromatids occurs at a region called the centromere.
Toward the end of prophase I in meiosis, homologous chromosomes appear as tetrads due to the presence of four sister chromatids, and the association between these homologous chromosomes starts to break down, although they remain connected at regions called chiasmata.
The nucleus undergoes significant changes during prophase as well, with the nucleolus fading and the nuclear envelope breaking down, preparing the cell for the subsequent stages of cell division.