the first stage in mitosis, during which the chromatin is formed into chromosomes which split into separate paired chromatids
Origin:
pro- + phase
See prophase in American Heritage Dictionary 4
noun
The first stage of mitosis, during which the chromosomes condense and become visible, the nuclear membrane breaks down, and the spindle apparatus forms at opposite poles of the cell.
The first stage of meiosis, constituted by a series of events that include the thickening and coiling of the chromosomes, synapsis of homologous chromosomes, tetrad formation, and crossing over.