![]() ![]() (See figure below, where meiosis I begins with a diploid (2 n = 4) cell and ends with two haploid ( n = 2) cells.) In humans (2 n = 46), who have 23 pairs of chromosomes, the number of chromosomes is reduced by half at the end of meiosis I ( n = 23).ĭuring prophase I, chromosomal condensation allows chromosomes to be viewed under the microscope. In addition, in meiosis I, the chromosomal number is reduced from diploid (2 n) to haploid ( n) during this process. Meiosis I is unique in that genetic diversity is generated through crossing over and random positioning of homologous chromosomes (bivalent chromosomes). Meiosis I proceeds directly to meiosis II without going through interphase. In meiosis I, the phases are analogous to mitosis: prophase I, metaphase I, anaphase I, and telophase I (below figure). The amount of DNA in the cell has doubled, and the ploidy of the cell remains the same as before, at 2 n. The steps leading up to meiosis are similar to those of mitosis – the centrioles and chromosomes are replicated. However, several features, namely, the pairing and genetic recombination between homologous chromosomes, are unique to meiosis. Meiosis uses similar mechanisms as those employed during mitosis to accomplish the separation and redistribution of chromosomes. Halving the ploidy in meiocytes is essential for restoring the genetic content of the zygote to that of the parents. Diploid (2 n) organisms rely on meiosis to produce meiocytes, which have half the ploidy of the parents, for sexual reproduction. Meiosis is the process by which replicated chromosomes undergo two nuclear divisions to produce four haploid cells, also called meiocytes (sperms and eggs). ![]()
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