What type of cell does mitosis occur in

Furthermore, when you consider all the possible pairings of male and female gametes, the variation in zygotes is 2 n 2 , which results in some fairly large numbers. But what about chromosome reassortment in humans? Humans have 23 pairs of chromosomes. That means that one person could produce 2 23 different gametes. In addition, when you calculate the possible combinations that emerge from the pairing of an egg and a sperm, the result is 2 23 2 possible combinations.

However, some of these combinations produce the same genotype for example, several gametes can produce a heterozygous individual. Of course, there are more than 23 segregating units Hirsch, While calculations of the random assortment of chromosomes and the mixture of different gametes are impressive, random assortment is not the only source of variation that comes from meiosis. In fact, these calculations are ideal numbers based on chromosomes that actually stay intact throughout the meiotic process.

In reality, crossing-over between chromatids during prophase I of meiosis mixes up pieces of chromosomes between homologue pairs, a phenomenon called recombination. Because recombination occurs every time gametes are formed, we can expect that it will always add to the possible genotypes predicted from the 2 n calculation. In addition, the variety of gametes becomes even more unpredictable and complex when we consider the contribution of gene linkage.

Some genes will always cosegregate into gametes if they are tightly linked, and they will therefore show a very low recombination rate. While linkage is a force that tends to reduce independent assortment of certain traits, recombination increases this assortment. In fact, recombination leads to an overall increase in the number of units that assort independently, and this increases variation.

While in mitosis, genes are generally transferred faithfully from one cellular generation to the next; in meiosis and subsequent sexual reproduction , genes get mixed up. Sexual reproduction actually expands the variety created by meiosis, because it combines the different varieties of parental genotypes.

Thus, because of independent assortment, recombination, and sexual reproduction, there are trillions of possible genotypes in the human species. During cell division, chromosomes sometimes disappear. This occurs when there is some aberration in the centromere , and spindle fibers cannot attach to the chromosome to segregate it to distal poles of the cell. Consequently, the lost chromosome never properly groups with others into a new nuclear envelope , and it is left in the cytoplasm , where it will not be transcribed.

Also, chromosomes don't always separate equally into daughter cells. This sometimes happens in mitosis, when sister chromatids fail to separate during anaphase. One daughter cell thus ends up with more chromosomes in its nucleus than the other. Likewise, abnormal separation can occur in meiosis when homologous pairs fail to separate during anaphase I. This also results in daughter cells with different numbers of chromosomes. The phenomenon of unequal separation in meiosis is called nondisjunction.

If nondisjunction causes a missing chromosome in a haploid gamete, the diploid zygote it forms with another gamete will contain only one copy of that chromosome from the other parent, a condition known as monosomy.

Conversely, if nondisjunction causes a homologous pair to travel together into the same gamete, the resulting zygote will have three copies, a condition known as trisomy Figure 3. The term " aneuploidy " applies to any of these conditions that cause an unexpected chromosome number in a daughter cell.

Aneuploidy can also occur in humans. For instance, the underlying causes of Klinefelter's syndrome and Turner's syndrome are errors in sex chromosome number, and Down syndrome is caused by trisomy of chromosome However, the severity of phenotypic abnormalities can vary among different types of aneuploidy.

In addition, aneuploidy is rarely transferred to subsequent generations, because this condition impairs the production of gametes. Overall, the inheritance of odd chromosome number arises from errors in segregation during chromosome replication. Often, it is these very exceptions or modifications of expected patterns in mitosis and meiosis that enrich our understanding of how the transfer of chromosomes is regulated from one generation to the next.

Belling, J. On the attachment of non-homologous chromosomes at the reduction division in certain chromosome daturas. Proceedings of the National Academy of Sciences 12 , 7—11 Farmer, J. On the maiotic phase reduction divisions in animals and plants.

Quarterly Journal of Microscopical Science 48 , — Open mitosis is one wherein the nuclear envelope disassembles, thereby, freeing the chromosomes. This is seen in animal and plant cells. Closed mitosis is when the nuclear envelope persists.

This is observed in fungi, certain protists, and many algae. Their chromosomes divide within an intact nucleus. Prokaryotes do not have mitosis.

However, their method of asexual reproduction is similar to the process of mitosis. Referred to as binary fission , the bacterial cell divides into two, which are clones of the original cell.

In multicellular eukaryotes, the stem cells are the type of cells that have not acquired a specific function yet. Instead, they divide indefinitely to produce more cells. In medicine and research, scientists culture them for use in stem cell treatments. Apart from stem cells, other mitotically active cells are progenitor cells and blast cells precursors. Both of them divide but not as indefinitely as the stem cells.

Cancer cells are another example. They are originally normal cells that eventually have lost control over their cell division and thus continue to proliferate. Schematic diagram and description of plant cells division. Notice how the plant cell divides. A phragmoplast forms in the center of the dividing cell.

Plants are characterized by having alternation of generations in their life cycles. This tutorial is a review of plant mitosis, meiosis, and alternation of generations. Read More. Plant cells have plastids essential in photosynthesis. They also have an additional layer called cell wall on their cell exterior. Although animal cells lack these cell structures, both of them have nucleus, mitochondria, endoplasmic reticulum, etc. Read this tutorial to learn plant cell structures and their roles in plants Humans are capable of only one mode of reproduction, i.

Haploid sex cells gametes are produced so that at fertilization a diploid zygote forms. This tutorial is an in-depth study guide regarding male and female reproductive physiology Stems primarily provide plants structural support.

This tutorial includes lectures on the external form of a woody twig and the origin and development of stems. Kevin Beck holds a bachelor's degree in physics with minors in math and chemistry from the University of Vermont.

Formerly with ScienceBlogs. More about Kevin and links to his professional work can be found at www. TL;DR Too Long; Didn't Read The take-home message is that both mitosis and meiosis are unique to eukaryotes ; binary fission is unique to prokaryotes but has several features in common with mitosis. In what type of cells does mitosis occur?

In eukaryotes, the only cells that undergo non-mitotic divisions are special gamete-producing cells in the gonads ovaries in women and testes in men. Mitosis is classically divided into four phases; many newer sources include five. In prophase , the chromosomes condense and the mitotic spindle tiny tubes consisting of proteins forms at each pole of the cell.

In prometaphase , the duplicated chromosome sets called sister chromatids migrate toward the midline of the cell. In metaphase, the chromosomes line up at the midline at the metaphase plate, with one sister chromatid in each pair on either side of this plate. In cells that are not actively dividing it is not easy to identify the chromosomes that carry the genetic information.

The DNA is a mass of loosely coiled threads. At this stage the DNA can be replicated. Once a cell starts to divide, the DNA becomes packaged more tightly so the chromosomes become shorter and denser. As they condense, chromosomes will take up stains allowing them to become visible under the light microscope. By the beginning of mitosis, the nucleosomes have coiled and supercoiled to produce the chromosome structure we can see under the microscope. The loose structure of DNA in a cell between divisions becomes organised into condensed structures visible under the microscope at the beginning of mitosis.