- The first phase of cell nucleus division, in which the chromosomes become visible, the cell nucleus starts to lose its identity, the mitotic spindle apparatus appears, and the centrioles migrate toward opposite poles.
Definition from: MeSH via Unified Medical Language System at the National Library of Medicine
- 1 : the initial stage of mitosis and of the mitotic division of meiosis characterized by the condensation of chromosomes consisting of two chromatids, disappearance of the nucleolus and nuclear membrane, and formation of the mitotic spindle.
2 : the initial stage of the first division of meiosis in which the chromosomes become visible, homologous pairs of chromosomes undergo synapsis and crossing-over, chiasmata appear, chromosomes condense with homologues visible as tetrads, and the nuclear membrane and nucleolus disappear and which is divided into the five consecutive stages leptotene, zygotene, pachytene, diplotene, and diakinesis.
Definition from: Merriam-Webster's Medical Dictionary by Merriam-Webster Inc.
See also Understanding Medical Terminology.