prophase The first phase of mitosis and meiosis I and meiosis II. In mitosis and the first division of meiosis the chromosomes become visible within the nucleus, coiling up to produce a series of compact spirals. In meiosis I they also undergo pairing during this phase, the phase then being divided into 5 successive stages: leptotene, zygotene, pachytene, diplotene, and diakinesis. The prophase of the second division of meiosis (prophase II) is very similar to prophase of mitosis: the nucleoli and nuclear membrane break down and the chromatids shorten and thicken. Many plants go directly from anaphase I to metaphase II and do not have a prophase II.

prophase The first stage of cell division, during which chromosomes contract and divide along their length (except for the centromeres) into chromatids. In mitosis, the chromosomes remain separate from each other. In the first division of meiosis, homologous chromosomes become paired (see pairing). By the end of first prophase the two chromosomes begin to move apart.

prophase The first phase of mitosis and meiosis, divided into prophase I and prophase II, during which the chromosomes become visible within the nucleus, coiling up to produce a series of compact spirals. In the first division of meiosis they also undergo pairing during this phase, the phase then being divided into five successive stages: leptotene, zygotene, pachytene, diplotene, and diakinesis.

prophase (proh-fayz) n. the first stage of mitosis and of each division of meiosis, in which the chromosomes become visible under the microscope.