Author: Daniel Zhou
Editors: Angela Pan and Peggy Yang
Artist: Jade Li
Mitosis and meiosis are the two ways cells reproduce. Mitosis occurs in somatic cells or any cell that isn’t a gamete. The process produces two identical cells with identical genes. The five phases are prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis. In the first phase, prophase, chromatin condenses into chromosomes. The chromosomes will look like two sister chromatids attached to the centromere. In the second phase, prometaphase, the nuclear envelope ruptures, and spindle fibers bind to the chromosomes. In the third phase, metaphase, the centrosomes of the spindle fibers move to opposite sides of the nucleus. The chromosomes are then lined up in the center. In the fourth phase, anaphase, the sister chromatids break apart and the chromosomes move to opposite sides of the cell. In part of the fifth phase, telophase, the nuclear envelope reforms, and DNA decondenses. As a result, two daughter nuclei form. In the last part, cytokinesis, the cell divides into two. In animal cells, this is accomplished through a cleavage furrow that cuts the cell in two. In plant cells, a cell plate is formed between the two that cuts the two daughter nuclei.
Meiosis is also known as reduction division. In the process, cells inherit one of each parent’s chromosomes. Meiosis is critical as it ensures that all organisms produced through sexual reproduction have the correct number of chromosomes. Meiosis has two parts, meiosis 1 and meiosis 2. These two parts have the same phases as mitosis but are done twice. Meiosis 1 is similar to mitosis, but in prophase 1, the chromosomes condense and pair up into tetrads. This allows the exchange of DNA in a process called crossing over, where DNA is lined up in the same spot. In metaphase 1, the tetrads line up in the middle, and then the chromosomes are separated in anaphase 1. In meiosis, telophase and cytokinesis are the same as in meiosis 1. There is then a brief period called interphase 2 between meiosis 1 and meiosis 2. Meiosis 2 is similar to mitosis. It will result in gamete cells with half the number of chromosomes as the starting cell had.
Citation:
Gottlieb SF, Gulani A, Tegay DH. Genetics, Meiosis. [Updated 2022 Aug 8]. In: StatPearls
[Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from:
https://www.ncbi.nlm.nih.gov/books/NBK482462/
Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York:
Garland Science; 2002. Mitosis. Available from:
https://www.ncbi.nlm.nih.gov/books/NBK26934/
Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York:
Garland Science; 2002. Meiosis. Available from:
https://www.ncbi.nlm.nih.gov/books/NBK26840/
Talking glossary of genomic and genetic terms. Talking Glossary of Genetic Terms | NHGRI.
(n.d.-a). https://www.genome.gov/genetics-glossary/Mitosis.
Talking glossary of genomic and genetic terms. Talking Glossary of Genetic Terms | NHGRI.
(n.d.-b). https://www.genome.gov/genetics-glossary/Meiosis.
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