prophase

[ proh-feyz ]

noun

1. Cell Biology. the first stage of mitosis or meiosis in eukaryotic cell division, during which the nuclear envelope breaks down and strands of chromatin form into chromosomes.

prophase

/ ˈprəʊˌfeɪz /

noun

1. the first stage of mitosis, during which the nuclear membrane disappears and the nuclear material resolves itself into chromosomes See also metaphase anaphase telophase
2. the first stage of meiosis, divided into leptotene, zygotene, pachytene, diplotene, and diakinesis phases

prophase

/ prō′fāz′ /

1. The first stage in the process of mitosis. Before prophase begins, the chromosomes duplicate to form two long, thin strands called chromatids. During prophase itself, the chromatids condense and thicken to form distinct bodies. Chromatids making up a single chromosome are joined at the middle in an area called the centromere. The membrane surrounding the nucleus disappears, and the spindle begins to form. In prophase and the later stages of mitosis until separation of the individual chromatids during anaphase, each chromosome consists of two chromatids, and each chromatid contains a complete copy of the genetic information belonging to the chromosome. For example, human beings have 23 pairs of chromosomes in all somatic cells, or 46 chromosomes in total. At the end of prophase, each of these 46 chromosomes contains two identical chromatids.
2. One of the two stages in meiosis that resemble prophase in mitosis. However, there are important distinctions between prophase of mitosis and prophase of meiosis. The prophase of meiosis occurring during the first meiotic division of the cell is usually called prophase I. In prophase I of meiosis, pairs of homologous chromosomes intertwine and the process called crossing over occurs as chromatids from homologous pairs of chromosomes swap genetic information. This process creates genetic diversity among the gametes formed through meiosis. In mitosis, by contrast, pairs of homologous chromosomes remain separate and there is no crossing over, since the purpose of mitosis is to produce cells with identical genetic material rather than gametes. At the beginning of prophase II of meiosis, which occurs after telophase during the first meiotic division, the chromosomes of each daughter cell are grouped together in a mass. During prophase II, the individual chromosomes of the daughter cells become distinct again and begin to prepare for the second meiotic division. If a membrane has formed around the chromosomes at the end of the first division, it disappears during prophase II.
3. See more at meiosis

Word History and Origins

Origin of prophase¹

First recorded in 1880–85; pro- ¹ + phase

Example Sentences

The prophase covers all changes up to the completion of the mitotic figure.

From Project Gutenberg

Figure 145 is a prophase showing the bivalent chromosomes still connected by linin fibers.

From Project Gutenberg

The first division is thus a reducing division, while the split appearing in the anaphase of the heterotype and presumably reappearing in the prophase of the homotype is the original split of the spireme thread.

From Project Gutenberg

In each case the tetrads are formed by the double longitudinal splitting of the chromosomes, the latter appearing in the prophase in the reduced number.

From Project Gutenberg

Figure 163 shows a somewhat later and more common prophase in which the unequal pair, one ring, crosses, and dumb-bells may be seen.

From Project Gutenberg