The mitotic prophase is very similar to Prophase II. In all meiosis, Prophase I is the most complex stage because homologous chromosomes have to pair and exchange genetic information. Meiosis usually has two cycles of segregation of chromosomes and thus twice undergoes prophase, leading to prophase I and prophase II. It requires two-division rounds that eventually result in four cells with just one copy of each paternal and maternal chromosome. It is a special form of cell division of germ cells. Sexually reproducing species use a process to produce gametes, such as sperm or egg cells, and this process is called meiosis. Sex chromosomes often undergo synapsis, but only one end of each sex chromosome contains the synaptonemal protein complex that binds the homologous chromosomes together. Then the chromosome's intervening regions are brought together and connected through a protein-RNA complex called the synaptonemal complex.ĭuring meiosis, autosomes undergo synapsis and are kept together by a protein complex called the synaptonemal complex along the entire length of the chromosomes. Then, aided by the extranuclear cytoskeleton, these end-membrane complexes migrate until matching ends have been paired. Their ends are first attached to the nuclear envelope once homologous chromosomes synapse. This occurs during prophase I of meiosis.
It enables the matching of homologous pairs and possible chromosomal crossover between them prior to their segregation. The pairing of two homologous chromosomes that occurs during meiosis is synapsis (also called syndesis). A protein complex known as the synaptonemal complex joins the paired chromosomes together. Synapsis occurs at multiple points in the random form. At the end of the chromosome, the synapsis process may begin and progress towards the centromere or vice-versa. Synapsis is a very specific and precise process. Homologous chromosomes (one from the mother and one from the father) come together and pair in the zygotene phase. It is followed by the stage of leptotene, where chromosome uncoiling and condensing occurs.
Zygotene comes under the second stage Prophase-1 of meiosis.
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