The phase following interphase and preceding metaphase of cell divisions (i.e. mitosis and meiosis), and in which during this phase the chromatin condenses (becoming more visible under a light microscope at high magnification) and initiating spindle formation
Cell divisions in eukaryotes, particularly mitosis and meiosis, are important since they give rise to new cells. Mitosis produces two cells that are genetically identical. Meiosis produces four cells that are genetically dissimilar and in which the chromosomes are reduced by half. Both mitosis and meiosis are comprised of chronological phases that start at prophase (followed by metaphase, anaphase, and finally by telophase). In meiosis though the prophase occurs twice, thus, the terms prophase I and prophase II.
During prophase of mitosis, the chromatin condenses, becoming more visible. This process is called chromatin condensation. The chromatin fibers condense to become distinct chromosomes that are visible when viewed under the light microscope at high magnification. Spindle formation begins and the nucleolus seems to disappear.
In meiosis, prophase occurs twice and referred to as prophase I and prophase II. Prophase I takes place in the first meiotic division and is comprised of the following sub-stages: leptotene, zygotene, pachytene, diplotene, and diakinesis. Prophase II has no similar sub-stages and occurs in second meiotic division. Nevertheless, both prophase I and prophase II are highlighted by the disappearance of the nucleoli and the nuclear envelope and chromatin condensation.
Word origin: Latin or Greek pró (before) + phase, phásis (“appearance”)
- cell cycle
- cell division