chromosome definition

Send us feedback. Mitotic metaphase chromosomes are best described by a linearly organized longitudinally compressed array of consecutive chromatin loops.[36]. DNA, found in the nuclei of cells and organised into chromosomes, is the substance that carries this information. See the full definition for chromosome in the English Language Learners Dictionary, Nglish: Translation of chromosome for Spanish Speakers, Britannica English: Translation of chromosome for Arabic Speakers, Britannica.com: Encyclopedia article about chromosome. These chromosomes display a complex three-dimensional structure, which plays a significant role in transcriptional regulation. On the other hand, they are so important that a special shorter name seems desirable. Plants important in agriculture such as tobacco or wheat are often polyploid, compared to their ancestral species. Chromosome puffs (seen in diagram) are diffused uncoiled regions of the polytene chromosome. [19], The prokaryotes – bacteria and archaea – typically have a single circular chromosome, but many variations exist. [77] Genetic counseling is offered for families that may carry a chromosome rearrangement. Investigation into the human karyotype took many years to settle the most basic question: How many chromosomes does a normal diploid human cell contain? borrowed from German Chromosom, from chromo- chromo- + -som -some entry 3, Note: Some genetic disorders are more common than others. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA). Dictionary.com Unabridged [87] Increased aneuploidy is often associated with increased DNA damage in spermatozoa. Chromosomal recombination during meiosis and subsequent sexual reproduction play a significant role in genetic diversity. One of the bodies (normally 46 in somatic cells in humans) in the cell nucleus that is the bearer of genes, has the form of a delicate chromatin filament during interphase, contracts to form a compact cylinder segmented into two arms by the centromere during metaphase and anaphase stages of cell divison, and is capable of reproducing its physical and chemical structure through successive cell divisons. All content on this website, including dictionary, thesaurus, literature, geography, and other reference data is for informational purposes only. In Drosophila melanogaster, for example, the chromosomes of the larval salivary glands undergo many rounds of endoreduplication. Prokaryotes do not possess nuclei. The number of plasmids in the cell is almost entirely determined by the rate of division of the plasmid – fast division causes high copy number. Chromosomes are thread-like molecules that carry hereditary information for everything from height to eye color. These are circular structures in the cytoplasm that contain cellular DNA and play a role in horizontal gene transfer. [ krō ′mə-sōm′ ] A structure in all living cells that consists of a single molecule of DNA bonded to various proteins and that carries the genes determining heredity. Chromosomes come in pairs: one set from the mother; the other set from the father. For example, they might get a genetic disorder like Down syndrome (extra chromosome 21) and Klinefelter syndrome (a male with two X chromosomes). Wheat has a haploid number of seven chromosomes, still seen in some cultivars as well as the wild progenitors. Chromosomes are made up of DNA and protein combined as chromatin. Weed Gave My Family Everything—Then Took It Away, New Finding That Testing Could Identify Defects in Fetuses Is a Genetics Baby Step. Bacterial chromosomes tend to be tethered to the plasma membrane of the bacteria. Asexually reproducing species have one set of chromosomes that are the same in all body cells. The term Chromosom was first suggested by the German anatomist Heinrich Wilhelm Gottfried von Waldeyer-Hartz in "Ueber Karyokinese und ihre Beziehungen zu den Befruchtungsvorgängen," Archiv für mikroskopische Anatomie, Band 23 (1888), p. 27: "In ester Linier möchte ich mir jedoch den Vorschlag erlauben, diejenigen Dinge, welche soeben mit Boveri als 'chromatische Elemente' bezeichnet wurden, an denen sich einer der wichtigsten Akten der Karyokinese, die Flemming'sche Längsteilung vollzieht, mit einem besonderen terminus technicus 'Chromosomen' zu belegen. The chromosomes, and therefore the genes, are made up of a chemical substance called DNA. These cells are then stained, photographed, and arranged into a karyogram, with the set of chromosomes arranged, autosomes in order of length, and sex chromosomes (here X/Y) at the end. The more-common pasta and bread wheat types are polyploid, having 28 (tetraploid) and 42 (hexaploid) chromosomes, compared to the 14 (diploid) chromosomes in the wild wheat.[66]. The American Heritage® Stedman's Medical Dictionary Published by Houghton Mifflin Harcourt Publishing Company. Eventually, complete proof came from chromosome maps in Morgan's own lab. The microtubules then pull the chromatids apart toward the centrosomes, so that each daughter cell inherits one set of chromatids. [16], In his famous textbook The Cell in Development and Heredity, Wilson linked together the independent work of Boveri and Sutton (both around 1902) by naming the chromosome theory of inheritance the Boveri–Sutton chromosome theory (the names are sometimes reversed). These, when combined by fertilisation, produce the new set of 23 pairs. In molecular biology application, this allows for its isolation from plasmid DNA by centrifugation of lysed bacteria and pelleting of the membranes (and the attached DNA). chromosome. Some of the early karyological terms have become outdated. From Simple English Wikipedia, the free encyclopedia. 'Chromatische Elemente' ist zu lang. There are 46 chromosomes in each human somatic cell organized in 23 pairs, of which 22 pairs are similar in appearance but differ at the molecular level. A defining feature of any chromosome is its compactness. Please tell us where you read or heard it (including the quote, if possible). When a male and a female gamete merge (fertilization), a new diploid organism is formed. Polytene chromosomes. Each chromosome contains many genes. Most eukaryotic chromosomes include packaging proteins called histones which, aided by chaperone proteins, bind to and condense the DNA molecule to maintain its integrity. Cells can be locked part-way through division (in metaphase) in vitro (in a reaction vial) with colchicine. These are XX in females and XY in males. Delivered to your inbox! In general, the karyotype is the characteristic chromosome complement of a eukaryote species. Usually, this will make the cell initiate apoptosis leading to its own death, but sometimes mutations in the cell hamper this process and thus cause progression of cancer. [3], Chromosomes are normally visible under a light microscope only during the metaphase of cell division (where all chromosomes are aligned in the center of the cell in their condensed form). For example, most eukaryotes are diploid, like humans who have 22 different types of autosomes, each present as two homologous pairs, and two sex chromosomes. [11][12] For example, Chromatin (Flemming 1880) and Chromosom (Waldeyer 1888), both ascribe color to a non-colored state. [76] Chimpanzees, the closest living relatives to modern humans, have 48 chromosomes as do the other great apes: in humans two chromosomes fused to form chromosome 2. Why Do “Left” And “Right” Mean Liberal And Conservative? Below is a table compiling statistics for the chromosomes, based on the Sanger Institute's human genome information in the Vertebrate Genome Annotation (VEGA) database. This reduces the 23 pairs (diploid) to 23 singles (haploid). [69] Plasmids and plasmid-like small chromosomes are, as in eukaryotes, highly variable in copy number. There are two kinds of sex chromosome, the X chromosome and the Y chromosome. Chromosomes come in pairs: one set from the mother; the other set from the father. When they duplicate, chromosomes look like the letter "X". Although the replication and transcription of DNA is highly standardized in eukaryotes, the same cannot be said for their karyotypes, which are often highly variable. The loops of 30-nm chromatin fibers are thought to fold upon themselves further to form the compact metaphase chromosomes of mitotic cells. These chromosomes display a complex three-dimensional structure, which plays a significant role in transcriptional regulation. Instead, their DNA is organized into a structure called the nucleoid. 'All Intensive Purposes' or 'All Intents and Purposes'? This page was last edited on 11 October 2020, at 00:25. [81] In particular, risk of aneuploidy is increased by tobacco smoking,[82][83] and occupational exposure to benzene,[84] insecticides,[85][86] and perfluorinated compounds. Accessed 17 Oct. 2020. These are called the autosomes. Prokaryote species generally have one copy of each major chromosome, but most cells can easily survive with multiple copies. Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020, Collins English Dictionary - Complete & Unabridged 2012 Digital Edition There are at least two such systems among the factors in the first chromosome in Drosophila. Prokaryotic chromosomes and plasmids are, like eukaryotic DNA, generally supercoiled. Histones are responsible for the first and most basic unit of chromosome organization, the nucleosome. Specialized cells undergo repeated rounds of DNA replication without cell division (endomitosis). Other organisms have more than two copies of their chromosome types, such as bread wheat, which is hexaploid and has six copies of seven different chromosome types – 42 chromosomes in total. This produces large amounts of glue before pupation. Often there is: Also, variation in karyotype may occur during development from the fertilized egg. anxiety caused by a dread of environmental perils, especially climate change.. the state of concern about the future of one's economic prospects. What made you want to look up chromosome? The mother's eggs always contain an X chromosome, while the father's sperm contains either a Y chromosome or an X chromosome. This information should not be considered complete, up to date, and is not intended to be used in place of a visit, consultation, or advice of a legal, medical, or any other professional. Prokaryotes may have more than one chromosome. Different animals have different numbers of chromosomes. If the name I propose is serviceable, it will become customary, otherwise it will soon pass into oblivion."). The shorter arms are called p arms (from the French petit, small) and the longer arms are called q arms (q follows p in the Latin alphabet; q-g "grande"; alternatively it is sometimes said q is short for queue meaning tail in French[35]). Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. A special DNA base sequence in the region of the kinetochores provides, along with special proteins, longer-lasting attachment in this region. A body in the cell nucleus (of which there are normally 46 in humans) that is a bearer of genes, has the form of a delicate chromatin filament during interphase, contracts to form a compact cylinder segmented into two arms by the centromere during metaphase and anaphase stages of cell divison, and is capable of reproducing its physical and chemical structure through successive cell divisons.

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