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Neocentromere
Neocentromeres are new centromeres that form at a place on the chromosome that is usually not centromeric. They typically arise due to disruption of the normal centromere. These neocentromeres should not be confused with “knobs”, which were also described as “neocentromeres” in maize in the 1950s. Unlike most normal centromeres, neocentromeres do not contain satellite sequences that are highly repetitive but instead consist of unique sequences. Despite this, most neocentromeres are still able to carry out the functions of normal centromeres in regulating chromosome segregation and inheritance. This raises many questions on what is necessary versus what is sufficient for constituting a centromere. As neocentromeres are still a relatively new phenomenon in cell biology and genetics, it may be useful to keep in mind that neocentromeres may be somewhat related to point centromeres, holocentromeres, and regional centromeres. Whereas point centromeres are defined by sequence, r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neocentromere Formation
Neocentromeres are new centromeres that form at a place on the chromosome that is usually not centromeric. They typically arise due to disruption of the normal centromere. These neocentromeres should not be confused with “knobs”, which were also described as “neocentromeres” in maize in the 1950s. Unlike most normal centromeres, neocentromeres do not contain satellite sequences that are highly repetitive but instead consist of unique sequences. Despite this, most neocentromeres are still able to carry out the functions of normal centromeres in regulating chromosome segregation and inheritance. This raises many questions on what is necessary versus what is sufficient for constituting a centromere. As neocentromeres are still a relatively new phenomenon in cell biology and genetics, it may be useful to keep in mind that neocentromeres may be somewhat related to point centromeres, holocentromeres, and regional centromeres. Whereas point centromeres are defined by sequence, re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Centromeres
The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids, creating a short arm (p) and a long arm (q) on the chromatids. During mitosis, spindle fibers attach to the centromere via the kinetochore. The physical role of the centromere is to act as the site of assembly of the kinetochores – a highly complex multiprotein structure that is responsible for the actual events of chromosome segregation – i.e. binding microtubules and signaling to the cell cycle machinery when all chromosomes have adopted correct attachments to the spindle, so that it is safe for cell division to proceed to completion and for cells to enter anaphase. There are, broadly speaking, two types of centromeres. "Point centromeres" bind to specific proteins that recognize particular DNA sequences with high efficiency. Any piece of DNA with the point centromere DNA sequence on it will typically form a centromere if p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Turner Syndrome
Turner syndrome (TS), also known as 45,X, or 45,X0, is a genetic condition in which a female is partially or completely missing an X chromosome. Signs and symptoms vary among those affected. Often, a short and webbed neck, low-set ears, low hairline at the back of the neck, short stature, and swollen hands and feet are seen at birth. Typically, those affected do not develop menstrual periods, or breasts without hormone treatment and are unable to have children without reproductive technology. Heart defects, diabetes, and low thyroid hormone occur in the disorder more frequently than average. Most people with Turner syndrome have normal intelligence; however, many have problems with spatial visualization that may be needed in order to learn mathematics. Vision and hearing problems also occur more often than average. Turner syndrome is not usually inherited; rather, it occurs during formation of the reproductive cells in a parent or in early cell division during developme ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mosaic (genetics)
Mosaicism or genetic mosaicism is a condition in multicellular organisms in which a single organism possesses more than one genetic line as the result of genetic mutation. This means that various genetic lines resulted from a single fertilized egg. Genetic mosaics may often be confused with chimerism, in which two or more genotypes arise in one individual similarly to mosaicism. In chimerism, though, the two genotypes arise from the fusion of more than one fertilized zygote in the early stages of embryonic development, rather than from a mutation or chromosome loss. Genetic mosaicism can result from many different mechanisms including chromosome nondisjunction, anaphase lag, and endoreplication. Anaphase lagging is the most common way by which mosaicism arises in the preimplantation embryo. Mosaicism can also result from a mutation in one cell during development, in which case the mutation will be passed on only to its daughter cells (and will be present only in certain adult ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Breakage-fusion-bridge Cycle
Breakage-fusion-bridge (BFB) cycle (also breakage-rejoining-bridge cycle) is a mechanism of chromosomal instability, discovered by Barbara McClintock in the late 1930s. Mechanism The BFB cycle begins when the end region of a chromosome, called its telomere, breaks off. When that chromosome subsequently replicates it forms two sister chromatids which both lack a telomere. Since telomeres appear at the end of chromatids, and function to prevent their ends from fusing with other chromatids, the lack of a telomere on these two sister chromatids causes them to fuse with one another. During anaphase the sister chromatids will form a bridge where the centromere in one of the sister chromatids will be pulled in one direction of the dividing cell, while the centromere of the other will be pulled in the opposite direction. Being pulled in opposite directions will cause the two sister chromatids to break apart from each other, but not necessarily at the site that they fused. This results in t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Myeloid Leukemia
Myeloid leukemia is a type of leukemia affecting myeloid tissue. Types include: * Acute myeloid leukemia * Chronic myelogenous leukemia * Acute megakaryoblastic leukemia * Blastic plasmacytoid dendritic cell neoplasm See also * Hematological malignancies * Myeloblast * transient myeloproliferative disease Transient myeloproliferative disease (TMD) occurs in a significant percentage of individuals born with the congenital genetic disorder, Down syndrome. It may occur in individuals who are not diagnosed with the syndrome but have some hematological c ... External links {{Set index article Leukemia lt:Mieloma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lung Cancer
Lung cancer, also known as lung carcinoma (since about 98–99% of all lung cancers are carcinomas), is a malignant lung tumor characterized by uncontrolled cell growth in tissues of the lung. Lung carcinomas derive from transformed, malignant cells that originate as epithelial cells, or from tissues composed of epithelial cells. Other lung cancers, such as the rare sarcomas of the lung, are generated by the malignant transformation of connective tissues (i.e. nerve, fat, muscle, bone), which arise from mesenchymal cells. Lymphomas and melanomas (from lymphoid and melanocyte cell lineages) can also rarely result in lung cancer. In time, this uncontrolled growth can metastasize (spreading beyond the lung) either by direct extension, by entering the lymphatic circulation, or via hematogenous, bloodborne spread – into nearby tissue or other, more distant parts of the body. Most cancers that originate from within the lungs, known as primary lung cancers, are carcinomas. The t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lipoma
A lipoma is a benign tumor made of fat tissue. They are generally soft to the touch, movable, and painless. They usually occur just under the skin, but occasionally may be deeper. Most are less than in size. Common locations include upper back, shoulders, and abdomen. It is possible to have a number of lipomas. The cause is generally unclear. Risk factors include family history, obesity, and lack of exercise. Diagnosis is typically based on a physical exam. Occasionally medical imaging or tissue biopsy is used to confirm the diagnosis. Treatment is typically by observation or surgical removal. Rarely, the condition may recur following removal, but this can generally be managed with repeat surgery. They are not generally associated with a future risk of cancer. Lipomas have a prevalence of roughly 2 out of every 100 people. Lipomas typically occur in adults between 40 and 60 years of age. Males are more often affected than females. They are the most common noncancerous so ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Homologous Recombination
Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may be also RNA in viruses). Homologous recombination is widely used by cells to accurately DNA repair harmful breaks that occur on both strands of DNA, known as double-strand breaks (DSB), in a process called homologous recombinational repair (HRR). Homologous recombination also produces new combinations of DNA sequences during meiosis, the process by which eukaryotes make gamete cells, like sperm and egg cells in animals. These new combinations of DNA represent genetic variation in offspring, which in turn enables populations to adapt during the course of evolution. Homologous recombination is also used in horizontal gene transfer to exchange genetic material between different strains and species of bacteria and viruses. Horizon ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isochromosome
An isochromosome is an unbalanced structural abnormality in which the arms of the chromosome are mirror images of each other. The chromosome consists of two copies of either the long (q) arm or the short (p) arm because isochromosome formation is equivalent to a simultaneous duplication and deletion of genetic material. Consequently, there is partial trisomy of the genes present in the isochromosome and partial monosomy of the genes in the lost arm. Nomenclature An isochromosome can be abbreviated as i(chromosome number)(centromeric breakpoint). For example, an isochromosome of chromosome 17 containing two q arms can be identified as i(17)(q10).(Medulloblastoma) Mechanism Isochromosomes can be created during mitosis and meiosis through a misdivision of the centromere or U-type strand exchange. Centromere misdivision Under normal separation of sister chromatids in anaphase, the centromere will divide longitudinally, or parallel to the long axis of the chromosome. An isoch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
