What kind of cells do meiosis

During pachynema and the next substage, diplonema, certain regions of synapsed chromosomes often become closely associated and swap corresponding segments of the DNA in a process known as chiasma. At this point, while still associated at the chiasmata, the sister chromatids start to part from each other although they are still firmly bound at the centromere; this creates the X-shape commonly associated with condensed chromosomes.

The nuclear membrane starts to dissolve by the end of diplonema and the chromosomes complete their condensation in preparation for the last substage of prophase I, diakinesis.

During this part, the chiasmata terminalize move toward the ends of their respective chromatids and drift further apart, with each chromatid now bearing some newly-acquired genetic material as the result of crossing over. Simultaneously, the centrioles, pairs of cylindrical microtubular organelles, move to opposite poles and the region containing them becomes the source for spindle fibers. These spindle fibers anchor onto the kinetochore, a macromolecule that regulates the interaction between them and the chromosome during the next stages of meiosis.

The kinetochores are attached to the centromere of each chromosome and help move the chromosomes to position along a three-dimensional plane at the middle of the cell, called the metaphase plate. The cell now prepares for metaphase I, the next step after prophase I. During metaphase I, the tetrads finish aligning along the metaphase plate, although the orientation of the chromosomes making them up is random. The chromosomes have fully condensed by the point and are firmly associated with the spindle fibers in preparation for the next step, anaphase I.

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. In each of the two daughter cells the chromosomes condense again into visible X-shaped structures that can be easily seen under a microscope. The membrane around the nucleus in each daughter cell dissolves away releasing the 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 is a fundamental process for life. During mitosis, a cell duplicates all of its contents, including its chromosomes, and splits to form two identical daughter cells. Because this process is so critical, the steps of mitosis are carefully controlled by certain genes. When mitosis is not regulated correctly, health problems such as cancer can result. The other type of cell division, meiosis, ensures that humans have the same number of chromosomes in each generation.

It is a two-step process that reduces the chromosome number by half—from 46 to 23—to form sperm and egg cells. By the end of meiosis, the resulting reproductive cells, or gametes , each have 23 genetically unique chromosomes. The overall process of meiosis produces four daughter cells from one single parent cell. Each daughter cell is haploid, because it has half the number of chromosomes as the original parent cell. Andrew Hoyt, a biologist and professor at Johns Hopkins University. Unlike in mitosis, the daughter cells produced during meiosis are genetically diverse.

Homologous chromosomes exchange bits of DNA to create genetically unique, hybrid chromosomes destined for each daughter cell. Before meiosis begins, some important changes take place within the parent cells. First, each chromosome creates a copy of itself.

These duplicated chromosomes are known as sister chromatids. They are fused together and the point where they are joined is known as the centromere. Fused sister chromatids roughly resemble the shape of the letter "X. Meiosis occurs over the course of two rounds of nuclear divisions, called meiosis I and meiosis II, according to Nature Education's Scitable.

Furthermore, meiosis I and II are each divided into four major stages: prophase, metaphase, anaphase and telophase. Meiosis I is responsible for creating genetically unique chromosomes. Sister chromatids pair up with their homologs and exchange genetic material with one another.

At the end of this division, one parent cell produces two daughter cells, each carrying one set of sister chromatids. Meiosis II closely resembles mitosis. The two daughter cells move into this phase without any further chromosome duplication. The sister chromatids are pulled apart during this division. A total of four haploid daughter cells are produced during the course of meiosis II.