During reproduction, when the sperm and egg unite to form a single cell, the number of chromosomes is restored in the offspring. Meiosis begins with a parent cell that is diploid, meaning it has two copies of each chromosome. The parent cell undergoes one round of DNA replication followed by two separate cycles of nuclear division. The process results in four daughter cells that are haploid, which means they contain half the number of chromosomes of the diploid parent cell.
Meiosis has both similarities to and differences from mitosis, which is a cell division process in which a parent cell produces two identical daughter cells. Meiosis begins following one round of DNA replication in cells in the male or female sex organs.
The process is split into meiosis I and meiosis II, and both meiotic divisions have multiple phases. Meiosis I is a type of cell division unique to germ cells, while meiosis II is similar to mitosis. Meiosis I, the first meiotic division, begins with prophase I. During prophase I, the complex of DNA and protein known as chromatin condenses to form chromosomes. The centrioles duplicate. The meiotic spindle forms again. Metaphase II: In each of the two daughter cells the chromosomes pair of sister chromatids line up end-to-end along the equator of the cell.
The centrioles are now at opposites poles in each of the daughter cells. Meiotic spindle fibres at each pole of the cell attach to each of the sister chromatids. Anaphase II: The sister chromatids are then pulled to opposite poles due to the action of the meiotic spindle. The separated chromatids are now individual chromosomes.
Telophase II and cytokinesis: The chromosomes complete their move to the opposite poles of the cell. A membrane forms around each set of chromosomes to create two new cell nuclei. This is the last phase of meiosis, however cell division is not complete without another round of cytokinesis. Once cytokinesis is complete there are four granddaughter cells, each with half a set of chromosomes haploid : in males, these four cells are all sperm cells in females, one of the cells is an egg cell while the other three are polar bodies small cells that do not develop into eggs.
Related Content:. What is a cell? What is a chromosome? What is mitosis? What is DNA? Mitosis versus meiosis. What is a genetic disorder? During anaphase I the sister chromatids move together to the same pole.
During anaphase II the sister chromatids are separated to opposite poles. Similarities Mitosis Diploid parent cell Consists of interphase, prophase, metaphase, anaphase and telophase In metaphase individual chromosomes pairs of chromatids line up along the equator. Ends with cytokinesis. Meiosis Diploid parent cell Consists of interphase, prophase, metaphase, anaphase and telophase but twice! In metaphase II individual chromosomes pairs of chromatids line up along the equator.
Related Content:. What is mitosis? The chromosomes arrive at opposite poles and begin to decondense. Nuclear envelopes form around the chromosomes. Cytokinesis separates the two cells into four unique haploid cells.
At this point, the newly-formed nuclei are both haploid. The cells produced are genetically unique because of the random assortment of paternal and maternal homologs and because of the recombining of maternal and paternal segments of chromosomes with their sets of genes that occurs during crossover.
Mitosis and meiosis share some similarities, but also some differences, most of which are observed during meiosis I. Mitosis and meiosis are both forms of division of the nucleus in eukaryotic cells.
They share some similarities, but also exhibit distinct differences that lead to very different outcomes. The purpose of mitosis is cell regeneration, growth, and asexual reproduction,while the purpose of meiosis is the production of gametes for sexual reproduction. Mitosis is a single nuclear division that results in two nuclei that are usually partitioned into two new daughter cells. The nuclei resulting from a mitotic division are genetically identical to the original nucleus.
They have the same number of sets of chromosomes, one set in the case of haploid cells and two sets in the case of diploid cells. In most plants and all animal species, it is typically diploid cells that undergo mitosis to form new diploid cells. In contrast, meiosis consists of two nuclear divisions resulting in four nuclei that are usually partitioned into four new haploid daughter cells.
The nuclei resulting from meiosis are not genetically identical and they contain one chromosome set only. This is half the number of chromosome sets in the original cell, which is diploid. Comparing Meiosis and Mitosis : Meiosis and mitosis are both preceded by one round of DNA replication; however, meiosis includes two nuclear divisions.
The four daughter cells resulting from meiosis are haploid and genetically distinct. The daughter cells resulting from mitosis are diploid and identical to the parent cell. The main differences between mitosis and meiosis occur in meiosis I. In meiosis I, the homologous chromosome pairs become associated with each other and are bound together with the synaptonemal complex.
Chiasmata develop and crossover occurs between homologous chromosomes, which then line up along the metaphase plate in tetrads with kinetochore fibers from opposite spindle poles attached to each kinetochore of a homolog in a tetrad. All of these events occur only in meiosis I. When the tetrad is broken up and the homologous chromosomes move to opposite poles, the ploidy level is reduced from two to one.
For this reason, meiosis I is referred to as a reduction division. There is no such reduction in ploidy level during mitosis. Meiosis II is much more similar to a mitotic division. In this case, the duplicated chromosomes only one set, as the homologous pairs have now been separated into two different cells line up on the metaphase plate with divided kinetochores attached to kinetochore fibers from opposite poles.
During anaphase II and mitotic anaphase, the kinetochores divide and sister chromatids, now referred to as chromosomes, are pulled to opposite poles. The two daughter cells of mitosis, however, are identical, unlike the daughter cells produced by meiosis. They are different because there has been at least one crossover per chromosome. Meiosis II is not a reduction division because, although there are fewer copies of the genome in the resulting cells, there is still one set of chromosomes, as there was at the end of meiosis I.
Meiosis II is, therefore, referred to as equatorial division. Privacy Policy. Skip to main content. Meiosis and Sexual Reproduction. Search for:. The Process of Meiosis. Introduction to Meiosis Meiosis is the nuclear division of diploid cells into haploid cells, which is a necessary step in sexual reproduction. Learning Objectives Describe the importance of meiosis in sexual reproduction.
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