What is the first phase of mitosis called?

The first phase of mitosis is known as prophase. During this stage, several key events occur that are crucial for the successful division of the cell. The chromatin, which is the relaxed form of DNA within the nucleus, condenses into visible chromosomes, each composed of two sister chromatids joined at the centromere. This condensation is essential as it allows the chromosomes to be accurately separated later in the process.

Additionally, during prophase, the nuclear envelope begins to break down, allowing the mitotic spindle, a structure made of microtubules, to begin forming and establishing connections with the chromosomes. The centrioles, which are involved in organizing the microtubules, move to opposite poles of the cell, further aiding in the formation of the spindle apparatus.

These processes set the stage for the next phases of mitosis, where the chromosomes will align, separate, and ultimately lead to the division of the cell into two identical daughter cells. Understanding prophase is crucial as it marks the transition from interphase, the phase where the cell prepares for division, to the active phases of mitosis.