What is the first phase of mitosis?

The first phase of mitosis is prophase, which is a critical stage in the cell division process. During prophase, chromatin condenses into distinct chromosomes, each consisting of two sister chromatids joined at a centromere. The nuclear envelope begins to break down, and the mitotic spindle starts to form, consisting of microtubules that will eventually help separate the sister chromatids. This phase is essential because it prepares the genetic material for the segregation that will occur in the later stages of mitosis.

In prophase, the chromosomes become visible under a microscope, marking a transition from the less organized chromatin structure present during interphase. The organization of chromosomes is vital for ensuring that each daughter cell will receive an identical set of chromosomes, thus maintaining genetic consistency. This foundational step sets the stage for the subsequent phases, where the actual separation of chromosomes takes place.