A chromosome is a deoxyribonucleic acid molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins which, aided by chaperone proteins, bind to and condense the DNA molecule to prevent it from becoming an unmanageable tangle; this three-dimensional genome structure plays a significant role in transcriptional regulation. Chromosomes are visible under a light microscope only when the cell is undergoing the metaphase of cell division. Before this happens, every chromosome is copied once, the copy is joined to the original by a centromere, resulting either in an X-shaped structure if the centromere is located in the middle of the chromosome or a two-arm structure if the centromere is located near one of the ends; the original chromosome and the copy are now called sister chromatids. During metaphase the X-shape structure is called a metaphase chromosome. In this condensed form chromosomes are easiest to distinguish and study. In animal cells, chromosomes reach their highest compaction level in anaphase during chromosome segregation.
Chromosomal recombination during meiosis and subsequent sexual reproduction play a significant role in genetic diversity. If these structures are manipulated incorrectly, through processes known as chromosomal instability and translocation, the cell may undergo mitotic catastrophe; 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. Some use the term chromosome in a wider sense, to refer to the individualized portions of chromatin in cells, either visible or not under light microscopy. Others use the concept in a narrower sense, to refer to the individualized portions of chromatin during cell division, visible under light microscopy due to high condensation; the word chromosome comes from the Greek χρῶμα and σῶμα, describing their strong staining by particular dyes. The term was coined by the German scientist von Waldeyer-Hartz, referring to the term chromatin, itself introduced by Walther Flemming, who discovered cell division.
Some of the early karyological terms have become outdated. For example and Chromosom, both ascribe color to a non-colored state; the German scientists Schleiden, Virchow and Bütschli were among the first scientists who first recognized the structures now familiar as chromosomes. In a series of experiments beginning in the mid-1880s, Theodor Boveri gave the definitive demonstration that chromosomes are the vectors of heredity, it is the second of these principles, so original. Wilhelm Roux suggested that each chromosome carries a different genetic configuration, Boveri was able to test and confirm this hypothesis. Aided by the rediscovery at the start of the 1900s of Gregor Mendel's earlier work, Boveri was able to point out the connection between the rules of inheritance and the behaviour of the chromosomes. Boveri influenced two generations of American cytologists: Edmund Beecher Wilson, Nettie Stevens, Walter Sutton and Theophilus Painter were all influenced by Boveri. In his famous textbook The Cell in Development and Heredity, Wilson linked together the independent work of Boveri and Sutton by naming the chromosome theory of inheritance the Boveri–Sutton chromosome theory.
Ernst Mayr remarks that the theory was hotly contested by some famous geneticists: William Bateson, Wilhelm Johannsen, Richard Goldschmidt and T. H. Morgan, all of a rather dogmatic turn of mind. Complete proof came from chromosome maps in Morgan's own lab; the number of human chromosomes was published in 1923 by Theophilus Painter. By inspection through the microscope, he counted 24 pairs, his error was copied by others and it was not until 1956 that the true number, 46, was determined by Indonesia-born cytogeneticist Joe Hin Tjio. The prokaryotes – bacteria and archaea – have a single circular chromosome, but many variations exist; the chromosomes of most bacteria, which some authors prefer to call genophores, can range in size from only 130,000 base pairs in the endosymbiotic bacteria Candidatus Hodgkinia cicadicola and Candidatus Tremblaya princeps, to more than 14,000,000 base pairs in the soil-dwelling bacterium Sorangium cellulosum. Spirochaetes of the genus Borrelia are a notable exception to this arrangement, with bacteria such as Borrelia burgdorferi, the cause of Lyme disease, containing a single linear chromosome.
Prokaryotic chromosomes have less sequence-based structure than eukaryotes. Bacteria have a one-point from which replication starts, whereas some archaea contain multiple replication origins; the genes in prokaryotes are organized in operons, do not contain introns, unlike eukaryotes. Prokaryotes do not possess nuclei. Instead, their DNA is organized into a structure called the nucleoid; the nucleoid occupies a defined region of the bacterial cell. This structure is, dynamic and is maintained and remodeled by the actions of a range of histone-like proteins, which associate with the bacterial chromosome. In archaea, the DNA in chromosomes is more organized, with the DNA packaged within structures similar to eukaryotic nucleosomes. Certain bacteria contain plasmids or other extrachromosomal DNA; these are circular structures in the cytoplasm that contain cellular
Marta Balletbò-Coll is a Catalan actress, film director, producer and cinematographer. Balletbò-Coll earned a degree in analytical chemistry from the Faculty of Chemistry of the University of Barcelona, worked as a journalist from 1982 to 1986, she subsequently worked as a translator in the United States, where she earned a Master's degree in cinematography from Columbia University in New York City on a Fulbright-LaCaixa scholarship. After Balletbò-Coll worked in multiple American advertising agencies, she founded Costabrava Films with Ana Simón Cerezo, with their first movie, Costa Brava, being released in 1995, successful at Frameline Film Festival. In 2006, she was awarded with the National Film Award of Catalonia, granted by the Generalitat de Catalunya for the production of her film Sévigné; the film won the grand prix of the Créteil International Women's Film Festival in 2006. 2004: Sévigné 1998: Cariño, he enviado los hombres a la luna! 1995: Costa Brava 1992: Intrepidíssima 1991: Harlequin Exterminator Butaca AwardsParis Lesbian and Feminist Film Festival Marta Balletbò-Coll on IMDb Costabrava Films Her profile on culturalianet.com Article about her in gaybarcelona.com The films of Marta Balletbò-Coll.
MAZ-7912/MAZ-7917 is a Soviet and Russian army 14×12 Twelve-wheel drive transporter-erector-launcher designed and developed by the Minsk Automobile Plant in Belarus. Developed for use as a Topol ICBM mobile launcher, the 7912 model is similar in design to the MAZ-547A but has seven axles instead of six, including one dead axle. In the mid-1980s, the MAZ-7917 variant was introduced, with an additional length of 1 m and crew cabins similar to the MAZ-7916 - and at present, the 8-axle MZKT-79221 variant is used to carry the Topol M, Topol's replacement. MAZ-7310 MZKT-79221 KAMAZ 7850 http://denisovets.ru/maz/mazpages/maz7917.html