Meiosis in which organs

During this third stage of meiosis I, the tetrads are pulled apart by the spindle fibers, each half becoming a dyad in effect, a chromosome or two sister chromatids attached at the centromere.

Assuming that nondisjunction failure of chromosomes to separate does not occur, half of the chromosomes in the cell will be maneuvered to one pole while the rest will be pulled to the opposite pole. This migration of the chromosomes is followed by the final and brief step of meiosis I, telophase I, which, coupled with cytokinesis physical separation of the entire mother cell , produces two daughter cells.

Each of these daughter cells contains 23 dyads, which sum up to 46 monads or single-stranded chromosomes. Meiosis II follows with no further replication of the genetic material. The chromosomes briefly unravel at the end of meiosis I, and at the beginning of meiosis II they must reform into chromosomes in their newly-created cells. This brief prophase II stage [isEmbeddedIn] is followed by metaphase II, during which the chromosomes migrate toward the metaphase plate.

During anaphase II, the spindle fibers again pull the chromosomes apart to opposite poles of the cell; however, this time it is the sister chromatids that are being split apart, instead of the pairs of homologous chromosomes as in the first meiotic step.

A second round of telophase this time called telophase II and cytokinesis splits each daughter cell further into two new cells. Each of these cells has 23 single-stranded chromosomes, making each cell haploid possessing 1N chromosomes. As mentioned, sperm and egg cells follow roughly the same pattern during meiosis , albeit a number of important differences. Spermatogenesis follows the pattern of meiosis more closely than oogenesis, primarily because once it begins human males start producing sperm at the onset of puberty in their early teens , it is a continuous process that produces four gametes per spermatocyte the male germ cell that enters meiosis.

Excluding mutation and mistakes, these sperm are identical except for their individual, unique genetic load. They each contain the same amount of cytoplasm and are propelled by whip-like flagella. In females, oogenesis and meiosis begin while the individual is still in the womb. The primary oocytes, analogous to the spermatocyte in the male, undergo meiosis I up to diplonema in the womb , and then their progress is arrested.

Once the female reaches puberty, small clutches of these arrested oocytes will proceed up to metaphase II and await fertilization so that they may complete the entire meiotic process; however, one oocyte will only produce one egg instead of four like the sperm. This can be explained by the placement of the metaphase plate in the dividing female germ cell. Instead of lying across the middle of the cell like in spermatogenesis, the metaphase plate is tucked in the margin of the dividing cell, although equal distribution of the genetic material still occurs.

This results in a grossly unequal distribution of the cytoplasm and associated organelles once the cell undergoes cytokinesis.

This first division produces a large cell and a small cell. Cytokinesis follows, dividing the cytoplasm of the two cells. At the conclusion of meiosis, there are four haploid daughter cells that go on to develop into either sperm or egg cells.

Further Exploration Concept Links for further exploration cell division replication metaphase anaphase telophase linkage chromosome cytokinesis haploid prometaphase principle of segregation principle of independent assortment spindle fibers gamete DNA chromatin nucleus cytoplasm eukaryote prophase recombination principle of segregation Principles of Inheritance. Related Concepts You have authorized LearnCasting of your reading list in Scitable. Do you want to LearnCast this session?

This article has been posted to your Facebook page via Scitable LearnCast. Change LearnCast Settings. Scitable Chat. Register Sign In. Meiosis occurs in the sex cells, so the sperm and egg cells in the human body, to create even more of themselves. Where does meiosis occur in the human body? Biology The Eukaryotic Cell Meiosis. Nam D. Apr 26, Imagine, for example, that eye color was controlled by a single gene, and that mom could have B, the allele for brown eyes or b, the allele for blue eyes, and dad could also have B or b.

This leads to four possibilities: You could get B from mom and B from dad, or B from mom and b from dad, or b from mom and B from dad, or b from mom and b from dad. Each sperm and egg will end up with either B or b from mom and either B or b from dad. It's a flip of the coin.

But this happens independently for each trait, so just because you got your dad's brown eyes doesn't mean you'll get his blond hair too. This shuffling process is known as recombination or "crossing over" and occurs while the chromome pairs are lined up in Metaphase I. In Metaphase I, homologous chromosome pairs line up. Homologous chromosomes can exchange parts in a process called "crossing over.