Meiosis occurs in diploid (2n) eukaryotes that reproduce sexually. Meiosis produces 4 haploid (n) daughter cells, each of which carries half of genetic material of their parents.
Prior to meiosis, cell has interphase. In this phase, there occurs material synthesis that is required for cell growth and cell preparation to generate division. During the phase, genetic information of a cell in the form of DNA undergoes replication.
in meiosis, there occurs 2 cell divisions consecutively. We call them as meiosis I and meiosis II. Each meiosis, whether it is meiosis I or meiosis II, occurs in some phases just like in mitosis. For better understanding, let us pay attention to the following explanation.
Meiosis I consists of prophase I, metaphase I, anaphase I, and Telophase I.
At the beginning of prophase I, chromosome duplicates and coils, so that it looks shorter and thicker. Each pair of chromosomes has double arms (tetrad) or a pair of twin chromatid. hr the phase, there occurs crossing over. Crossing over is a process where chromosome arms crisscross with the homologous chromosomes. It can cause gene exchange and produce genetic recombination. The site where crossing over occurs is called chiasma.
|Meiosis I and its stages|
Nucleolus then disappears in cytoplasm. Spindle is formed between two pairs of centrioles when the two of them move to the opposite pole. At the end of prophase I, nucleus membrane disappears.
In metaphase I, the two pairs of centrioles have already been in opposite pole. The pair of homologous of chromosomes are arranged in metaphase plate (equator plate) and each of the chromosomes attaches to spindle.
Anaphase I begins when chromosome pairs separate and start to move to opposite pole. In this process, the twin chromatid still attach to the centromere and move simultaneously toward the pole.
In this phase, each pole has one set of chromosomes. Each chromosome still has two chromatid. Nucleus membrane is formed, and it surrounds each set of chromosome. Spindle disappears, and it is followed by cytokinesis.
source: biology of life 2006.