Prophase

Definition

noun

The first phase 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


Supplement

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, and prophase I and prophase II of meiosis, 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 I is comprised of the following sub-stages:


Word origin: Latin or Greek pró (before) + phase

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