prófase

Prófase is the initial stage of mitosis and meiosis, the processes of cell division in eukaryotic organisms. It is characterized by the condensation of chromatin into visible chromosomes. During prófase, the nuclear envelope begins to break down, and the nucleolus disappears. In animal cells, the centrosomes, which are involved in organizing microtubules, move to opposite poles of the cell. These centrosomes then form the mitotic spindle, a structure composed of microtubules that will eventually attach to the chromosomes.

As prófase progresses, the chromosomes become shorter and thicker, making them easier to observe under a microscope. Each chromosome consists of two identical sister chromatids, which are joined together at a region called the centromere. The breakdown of the nuclear envelope allows the spindle fibers to access the chromosomes within the former nuclear region. This stage is crucial for ensuring that each daughter cell receives a complete set of genetic material. The events of prófase set the stage for the subsequent phases of cell division, prometaphase, metaphase, anaphase, and telophase.