What is Mitosis?
In cell biology, the process of mitosis is a phase of the cell cycle , in which duplicated chromosomes are divided into two nuclei. Cell division creates cells that are genetically identical, in which the number of chromosomes are maintained. Thus, mitosis is called equational division. In general the case of mitosis, it begins with S stage of interphase (during the time that DNA replication occurs) and is usually followed by cytokinesis and telophase that divides the organelles, cytoplasm and cell membrane of a cell into two cells that contain roughly equal amounts of the cellular components. Different stages of mitosis together are the basis for what is known as the Mitotic (M) period of the animal cell cycle, which is the split of the cell’s mother into daughter cells that are genetically identical to one another.
Mitosis can be divided into stages that correspond to the conclusion of one set of actions and the commencement with the following. These stages are called preprophase (specific to cells of the plant) prophase metaphase, prometaphase anaphase, and finally telophase. In mitosis the chromosomes, that already duplicated, expand and connect to spindle fibers which draw one copy of each chromosome onto different sides in the cell. The result is two identical daughters nuclei. The remainder of the cell can then grow by cytokinesis, resulting in twin cells. The various stages of mitosis are visible in real-time with real-time imaging of cells. Producing more than three daughter cells in addition to the normal two cells is a mitotic mistake known as tripolar mitosis or multipolar mitosis (direct cell multiplication or triplication). Other mitosis-related errors can cause the process of apoptosis (programmed cells dying) or lead to mutations. Certain types of cancer may be caused by these mutations.
Mitosis is only seen in the eukaryotic cells. Prokaryotic cells, lacking nucleus, split by another process known as binary fission. The process of mitosis differs between different organisms. For instance animal cells go through the process of “open” mitosis process, in which the nuclear envelope is broken down before the chromosomes split while fungi go through an “closed” mitosis, in which the chromosomes are split inside an intact nucleus of the cell. Animal cells generally undergo a morphological change called mitotic cell rounding. They change to a spherical shape during the beginning of mitosis. The majority of human cells are created through mitotic division of cells. The gametes are the only exceptions eggs and sperm cells, which are created through meiosis.
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What is Meiosis?
Meiosis (from the Ancient Greek meiosis (meiosis) meaning ‘lessening’ due to its reductional division) is a particular kind of division of germ cells within sexually reproducing organisms that create gametes, like egg cells or sperm. It is a two-stage division, which ultimately produce four cells that have only one copy of each one of the chromosomes (haploid). Furthermore, prior to division, the genetic material of paternal and maternal versions of every chromosome are cross-bred, resulting in new codes on every one of the chromosomes. After fertilization of haploid cells, the cells created through meiosis between a male and female will re-join to form a cell that has the two copies for each chromosome called the zygote.
Meiosis errors that cause aneuploidy (an abnormality in the quantity of chromosomes) are the most widely known reason for miscarriage and is the most frequently cited genetic causes of developmental disabilities.
Meiosis is a process where DNA replication follows by 2 cycles of cell division that create four daughter cells, each having less than half of the number of chromosomes that the parent cell. The two meiotic divisions are identified as meiosis I as well as meiosis II. Prior to meiosis beginning, during the S stage of cell development the DNA of every chromosome is replicated , resulting in the formation in two sister chromatids that are identical which are held together by cohesion between sister chromatids. The S-phase is often called “premeiotic S-phase” or “meiotic S-phase”. Following the replication of DNA meiotic cells go through an extended G2-like phase called meiotic prophase.
In this period homologous chromosomes mate with one another through genetic recombination an automated process through which DNA is broken and then repaired, which permits the exchange of parts of their genetic information. Recombination that is not complete causes crossovers, which result in physical connections known as Chiasmata (singular name: chiasma for the Greek letter Chi (Kh)) between homologous chromosomes. In the majority of organisms, these links aid in directing each pair homologous chromosomes away from one another in Meiosis I, resulting in two haploid cells which have only half as many chromosomes of the parent cell.
During meiosis II the cohesion of sister chromatids becomes dispersed and they are segregated from one another as when mitosis occurs. In certain instances there are instances where all four meiotic products are transformed into gametes, such as spores, sperm or pollen. Female animals have three of the meiotic substances are usually destroyed by extrusion into the body polars, and only one of them develops into an Ovum. Since that the amount of chromosomes decreased by meiosis. Gametes are able to join (i.e. fertilization) to create an zygote with diploids that contain the chromosomes in two different copies two copies from the parent.
Therefore, the alternating cycles of meiosis and fertilization allow reproductive sexuality, which results in subsequent generations keeping the same number of chromosomes. For instance the human diploid cells have 23 different chromosomes that include one pair of sex chromosomes (46 total) 50% of them are of maternal and half from paternal origin. Meiosis results in games with haploids (ova or sperm) with 23 chromosomes.
If two gametes (an egg and the sperm) join, the resultant embryo is again a diploid with father and mother each providing 23 chromosomes. The same pattern, although not the exact number of chromosomes, is seen in all organisms that use meiosis.
Meiosis is a common occurrence in sexually reproducing multicellular and single-celled organisms (which comprise all eukaryotes) which includes animals plants, fungi and plants. It is a crucial process for oogenesis as well as spermatogenesis.
Differences between Mitosis and Meiosis – Mitosis vs Meiosis
|Alternate Name||Equational Division||Reduction Division|
|Discovered by||Walther Flemming||Oscar Hertwig|
|Type of Cells Involved||Somatic cells.||Sex cells/germ cells , or gametes.|
|Type of Reproduction||Asexual division||Sexual division|
|Mother Cells||It can be either diploloid or haploid.||Always diploid|
|Number of Divisions||Mitosis only affects one cell division.||Involves two successive divisions.|
|The number of cells with daughter cells||Two||Four|
|The result will be||Diploid (2n) offspring||Haploid (n) offspring|
|Reduction in Chromosome Number||There is no reduction in the number of chromosomes.||This results in a reduction of the number of chromosomes to half.|
|Genetical Identity||Daughter cells are genetically identical.||Daughter cells differ genetically because of Recombination.|
|The process of crossing or recombination||There is no crossing or recombination that occurs.||Crossing over occurs.|
|The process leads to the formation of||Anything else than sex cell.||Sex cells are female egg cells and male Sperm cells.|
|Steps Involved||Prophase, Metaphase, Anaphase, Telophase.||(Meiosis 1) Prophase I, Metaphase I, Anaphase I, Telophase I; (Meiosis 2) Prophase II, Metaphase II, Anaphase II and Telophase II.|
|Interphase||Interphase takes place before each division.||Interphase occurs in the absence of Meiosis I. It is not present before Meiosis II.|
|DNA replication during Interphase||Takes place during Interphase.||Takes place during Interphase I but not during Interphase II.|
|DNA replication||It occurs only once per cell division.||It occurs once for 2 cell divisions.|
|Steps and Length of Prophase||A cell has less time in the prophase of mitosis stage than cells in meiosis in prophase I.Sub-stages are not present in mitosis.||Prophase I consists of five stages, and is longer than mitosis’ prophase. Five stages in meiotic phase I include leptotene and pachytene and zygotene as well as diplotene and diakinesis.|
|Synapsis||There isn’t a synapse||The synapses of homologous chromosomes take place during the prophase.|
|Tetrad Formation||Tetrad formation is not a common thing.||A tetrad containing 4 the chromatids (two set of sisterchromatids) that are closely arranged is created.|
|Centromere||Each chromosome has two chromatids that are joined by the centromere.||Two homologous chromosomes are formed into bivalents, also known as Tetrads. Each bivalent is composed of four chromatids, and two centromeres.|
|Metaphase||Sister chromatids form a line on their metaphase plates (a plane that is also distant from the electrodes of the cell).||Tetrads (homologous chromosome pairs) meet at the metaphase plate during metaphase I.|
|Chromosome Alignment in Metaphase||On the plate of metaphase all the centromeres align on the one plate.||In metaphase I the centromeres are lined into two planes, which are parallel to each other.|
|Chiasmata||Absent||It was observed during prophase I as well as metaphase I.|
|Anaphase||Sister chromatids are separated and then begin to migrate centromeres first towards two opposite sides of the cell. A sister chromatid separated from the cell is known as a daughter chromosome and is considered to be a full chromosome.||Anaphase I is when (double stranded) the chromosomes are split off towards the cellular poles. Sister chromatids don’t separate in anaphase I.On the contrary, (single stranded) chromosomes are those that are segregated in anaphase II.|
|Centromeres Split||The centromeres split during anaphase.||The centromeres are not separated in anaphase I but in anaphase II.|
|Spindle Fibres||In telophase, they disappear completely.||Do not disappear completely from the telophase I.|
|Nucleoli||Reappear at telophase.||Do not appear again at the telophase I.|
|Karyokinesis||Occurs in Interphase.||Occurs in Interphase I.|
|Cytokinesis (division of the celluplasm)||It occurs at the beginning of telophase.||Cytokinesis occurs at the end of telophase I and II.|
|Functions||Help in growth, repairs and replacement.In order to produce more cells, especially in the initial stage of the development.To repair damaged and destroyed cells.Mitosis can also be found also in protokaryotes in a crucial type of reproductive asexuality.||Participates in the development of gametes.To keep the chromosome number of offspring.To ensure the preservation of genetic diversity, which is what natural selection is based.|