Diagram of a duplicated and condensed (metaphase) eukaryotic chromosome. Metaphase from the Ancient Greek μετά (after and φάσις (stage is a stage of Mitosis in the eukaryotic Cell cycle in which (1) Chromatid - one of the two identical parts of the chromosome after S phase. A chromatid is one of two identical copies of DNA making up a replicated Chromosome, which are joined at their Centromeres for the process of Cell division The S phase, short for synthesis phase, is a period in the Cell cycle during Interphase, between G1 phase and the G2 phase. (2) Centromere - the point where the two chromatids touch, and where the microtubules attach. A centromere is a region of DNA typically found near the middle of a Chromosome where two Sister chromatids come in contact (3) Short arm. (4) Long arm.

Chromosomes are organized structures of DNA and proteins that are found in cells. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called A chromosome is a singular piece of DNA, which contains many genes, regulatory elements and other nucleotide sequences. History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance A regulatory sequence (also called a regulatory region or a regulatory area) is a segment of DNA where regulatory proteins such as Transcription A DNA sequence or genetic sequence is a succession of letters representing the Primary structure of a real or hypothetical DNA Molecule Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions. The word chromosome comes from the Greek χρῶμα (chroma, color) and σῶμα (soma, body) due to their property of being stained very strongly by some dyes. Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly A dye can generally be described as a Colored substance that has an affinity to the substrate to which it is being applied

Chromosomes vary extensively between different organisms. The DNA molecule may be circular or linear, and can contain anything from tens of kilobase pairs to hundreds of megabase pairs. In Molecular biology, two Nucleotides on opposite complementary DNA or RNA strands that are connected via Hydrogen bonds are called A megabase (Mb is a unit of length for DNA fragments equal to 1 million Nucleotides In the Human genome, one megabase is roughly equivalent to one Typically eukaryotic cells (cells with nuclei) have large linear chromosomes and prokaryotic cells (cells without defined nuclei) have smaller circular chromosomes, although there are many exceptions to this rule. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other Furthermore, cells may contain more than one type of chromosome; for example mitochondria in most eukaryotes and chloroplasts in plants have their own small chromosomes. In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex Chloroplasts are Organelles found in Plant cells and eukaryotic Algae that conduct Photosynthesis.

In eukaryotes, nuclear chromosomes are packaged by proteins into a condensed structure called chromatin. Chromatin is the complex basis of DNA and protein that makes up Chromosomes It is found inside the nuclei of eukaryotic cells, and within the This allows the very long DNA molecules to fit into the cell nucleus. In Cell biology, the nucleus (pl nuclei; from Latin la ''nucleus'' or la ''nuculeus'' "little nut" or kernel is a membrane-enclosed The structure of chromosomes and chromatin varies through the cell cycle. The cell cycle, or cell-division cycle, is the series of events that take place in a eukaryotic cell leading to its replication Chromosomes may exist as either duplicated or unduplicated—unduplicated chromosomes are single linear strands, while duplicated chromosomes (copied during synthesis phase) contain two copies joined by a centromere. The S phase, short for synthesis phase, is a period in the Cell cycle during Interphase, between G1 phase and the G2 phase. A centromere is a region of DNA typically found near the middle of a Chromosome where two Sister chromatids come in contact Compaction of the duplicated chromosomes during mitosis and meiosis results in the classic four-arm structure (pictured to the right). Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half

"Chromosome" is a rather loosely defined term. In prokaryotes, a small circular DNA molecule may be called either a plasmid or a small chromosome. A plasmid is an extra-chromosomal DNA molecule separate from the chromosomal DNA which is capable of replicating independently of the chromosomal DNA These small circular genomes are also found in mitochondria and chloroplasts, reflecting their bacterial origins. The simplest chromosomes are found in viruses: these DNA or RNA molecules are short linear or circular chromosomes that often lack any structural proteins. A virus (from the Latin virus meaning Toxin or Poison) is a sub-microscopic infectious agent that is unable

History

This is a brief history of research in a complex field where each advance was hard won, and often hotly disputed at the time.

Visual discovery of chromosomes. Textbooks have often said that chromosomes were first observed in plant cells by a Swiss botanist named Karl Wilhelm von Nägeli in 1842. Plants are living Organisms belonging to the kingdom Plantae. Switzerland (English pronunciation; Schweiz Swiss German: Schwyz or Schwiiz Suisse Svizzera Svizra officially the Swiss Confederation Botany, plant science(s, phytology, or plant biology is a branch of Biology and is the scientific study of plant Life Karl Wilhelm von Nägeli ( March 27, 1817 – May 11, 1891) was a Swiss botanist. Year 1842 ( MDCCCXLII) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian Calendar (or a Common ^[1] However, this opinion has been challenged, perhaps decisively, by Henry Harris, who has freshly reviewed the primary literature. Sir Henry Harris, FRS, (born January 28 1925) is an Australian-born professor of Medicine at Oxford University ^[2] In his opinion the claim of Nägeli to have seen spore mother cells divide is mistaken, as are some of his interpretations. Harris considers other candidates, especially Wilhelm Hofmeister, whose publications in 1848-9 include plates which definitely show mitotic events. Wilhelm Friedrich Benedikt Hofmeister ( 18 May 1824 to 12 January 1877) was a German Biologist and Botanist ^[3][4] Hofmeister was also the choice of Cyril Darlington. Cyril Dean Darlington ( 19 December 1903 - 26 March 1981) was an English Biologist,

The work of other cytologists such as Walther Flemming, Eduard Strasburger, Otto Bütschli, Oskar Hertwig and Carl Rabl should definitely be acknowledged. Walther Flemming ( April 21[[ 843]] - August 4[[ 905]] was a German Biologist and the founder of Cytogenetics. Eduard Adolf Strasburger ( February 1, 1844, Warsaw &ndash May 19, 1912 Bonn) was a Polish - German Johann Adam Otto Bütschli ( 3 May 1848, Frankfurt &ndash 2 February 1920, Heidelberg) was a German Zoologist Oscar Hertwig ( April 21, 1849, Friedberg, Hesse - October 25, 1922, Berlin) was a German Zoologist Carl Rabl was an Austrian anatomist His most notable achievement was on the structural consistency of Chromosomes during the Cell cycle. The use of basophilic aniline dyes was a new technique for effectively staining the chromatin material in the nucleus. Basophilic is a technical term used by histologists. It describes the microscopic appearance of cells and tissues as seen down the Microscope, Aniline, phenylamine or aminobenzene is an Organic compound with the formula C6H7N A dye can generally be described as a Colored substance that has an affinity to the substrate to which it is being applied Staining is an auxiliary Technique used in Microscopy to enhance contrast in the microscopic image Chromatin is the complex basis of DNA and protein that makes up Chromosomes It is found inside the nuclei of eukaryotic cells, and within the Their behavior in animal (salamander) cells was later described in detail by Walther Flemming, who in 1882 "provided a superb summary of the state of the field". Salamander (orig from Persian: sām, "fire" and andarūn, "within" is the common name for a group of approximately 500 Species Walther Flemming ( April 21[[ 843]] - August 4[[ 905]] was a German Biologist and the founder of Cytogenetics. ^[5][6] The name chromosome was invented in 1888 by Heinrich von Waldeyer. Heinrich Wilhelm Gottfried von Waldeyer-Hartz ( October 6, 1836, Hehlen an der Weser, Braunschweig, Germany – January 23 However, van Beneden's monograph of 1883 on the fertilised eggs of the parasitic roundworm Ascaris megalocephala was the outstanding work of this period. Ascaris is a genus of parasitic Nematode worms One species A suum, typically infects Pigs, while another ^[7] His conclusions are classic:

• Thus there is no fusion between the male chromatin and the female chromatin at any stage of division. . .
• The elements of male origin and those of female origin are never fused together in a cleavage nucleus, and perhaps they remain distinct in all the nuclei derived from them. [tranl: Harris p162]

"It is not easy to identify who first discerned chromosomes during mitosis, but there is no doubt that those who first saw them had no idea of their significance. . . [but] with the work of Balbiani and van Beneden we move away from. Edouard-Gérard Balbiani ( July 31, 1823 - July 25, 1899 was a French embryologist who was born in Port-au-Prince, Haiti Edouard Van Beneden ( 5 March, 1846, Leuven – 28 April, 1910, Liège) son of Pierre-Joseph Van Beneden, was . . the mechanism of cell division to a precise delineation of chromosomes and what they do during the division of the cell. " ^[8]

Van Beneden's master work was closely followed by that of Carl Rabl, who reached similar conclusions. ^[9] This more or less concludes the first period, in which chromosomes were visually sighted, and the morphological stages of mitosis were described. Coleman also gives a useful review of these discoveries. ^[10]

Nucleus as the seat of heredity. The origin of this epoch-making idea lies in a few sentences tucked away in Ernst Haeckel's Generelle Morphologie of 1866. ^[11] The evidence for this insight gradually acumulated until, after twenty or so years, two of the greatest in a line of great German scientists spelt it out. August Weismann proposed that the germ line was separate from the soma, and that the cell nucleus was the repository of the hereditary material, which he proposed was arranged along the chromosomes in a linear manner. Friedrich Leopold August Weismann (Birth January 17, 1834 in Frankfurt am Main; Death In Biology and Genetics, the germline of a mature or developing individual is the line (sequence of Germ cells that have genetic material that Somatic cells are any cells forming the body of an organism as opposed to Germline cells Furthermore, he proposed that at fertilisation a new combination of chromosomes (and their hereditary material) would be formed. This was the explanation for the reduction division of meiosis (first described by van Beneden). In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half

Chromosomes as vectors of heredity. In a series of outstanding experiments, Theodor Boveri gave the definitive demonstration that chromosomes were the vectors of heredity. Theodor Heinrich Boveri ( October 12, 1862 &ndash October 15, 1915) was a German Biologist whose work with Sea urchins His two principles were:

The continuity of chromosomes

The individuality of chromosomes.

It was the second of these principles which was so original. He was able to test the proposal put forward by Wilhelm Roux, that each chromosome carries a different genetic load, and showed that Roux was right. Wilhelm Roux ( June 9, 1850 &ndash September 15, 1924) was a German zoologist and pioneer of experimental Embryology Upon the rediscovery of Mendel, Boveri was able to point out the connection between the rules of inheritance and the behaviour of the chromosomes. It is interesting to see that Boveri influenced two generations of American cytologists: Edmund Beecher Wilson, Walter Sutton and Theophilus Painter were all influenced by Boveri (Wilson and Painter actually worked with him). Edmund Beecher Wilson ( October 19, 1856 – March 3, 1939) was a pioneering American Zoologist and Geneticist Biography Early life Sutton was born at Utica New York, and was raised in Russell Kansas. Theophilus Shickel Painter ( August 22, 1889 &ndash October 5, 1969) was an American zoologist known for his work in identifying In his famous textbook The Cell, Wilson linked Boveri and Sutton together by the Boveri-Sutton theory. The Boveri-Sutton chromosome theory is that Mendelian alleles are located on Chromosomes. 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. William Bateson ( Robin Hood's Bay, August 8 1861 &ndash February 8 1926 was a British Geneticist, a Fellow of St Wilhelm Johannsen ( February 3, 1857 - November 11, 1927) was a Danish Botanist, plant physiologist and Geneticist Richard Benedict Goldschmidt ( April 12, 1878 – April 24, 1958) was a German -born American Geneticist. Thomas Hunt Morgan ( September 25, 1866 &ndash December 4, 1945) was an American geneticist and embryologist. Eventually complete proof came from chromosome maps – in Morgan's own lab! ^[12]

Chromosomes in eukaryotes

Eukaryotes (cells with nuclei such as plants, yeast, and animals) possess multiple large linear chromosomes contained in the cell's nucleus. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called Each chromosome has one centromere, with one or two arms projecting from the centromere, although under most circumstances these arms are not visible as such. A centromere is a region of DNA typically found near the middle of a Chromosome where two Sister chromatids come in contact In addition most eukaryotes have a small circular mitochondrial genome, and some eukaryotes may have additional small circular or linear cytoplasmic chromosomes. In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. The cytoplasm is the contents of a cell that is enclosed within the Plasma membrane.

In the nuclear chromosomes of eukaryotes, the uncondensed DNA exists in a semi-ordered structure, where it is wrapped around histones (structural proteins), forming a composite material called chromatin. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex In Biology, histones are the chief Protein components of Chromatin. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Chromatin is the complex basis of DNA and protein that makes up Chromosomes It is found inside the nuclei of eukaryotic cells, and within the

Chromatin

Main article: Chromatin

Fig. Chromatin is the complex basis of DNA and protein that makes up Chromosomes It is found inside the nuclei of eukaryotic cells, and within the 2: The major structures in DNA compaction; DNA, the nucleosome, the 10nm "beads-on-a-string" fibre, the 30nm fibre and the metaphase chromosome. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known Nucleosomes form the fundamental repeating units of eukaryotic Chromatin, which is used to pack the large eukaryotic genomes into the nucleus while still ensuring Metaphase from the Ancient Greek μετά (after and φάσις (stage is a stage of Mitosis in the eukaryotic Cell cycle in which

Chromatin is the complex of DNA and protein found in the eukaryotic nucleus which packages chromosomes. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex The structure of chromatin varies significantly between different stages of the cell cycle, according to the requirements of the DNA. The cell cycle, or cell-division cycle, is the series of events that take place in a eukaryotic cell leading to its replication

Interphase chromatin

During interphase (the period of the cell cycle where the cell is not dividing) two types of chromatin can be distinguished:

• Euchromatin, which consists of DNA that is active, e. Interphase is the phase of the Cell cycle in which the cell spends the majority of its time and performs the majority of its purposes including preparation for Cell The cell cycle, or cell-division cycle, is the series of events that take place in a eukaryotic cell leading to its replication Chromatin is the complex basis of DNA and protein that makes up Chromosomes It is found inside the nuclei of eukaryotic cells, and within the Euchromatin is a lightly packed form of Chromatin that is rich in Gene concentration and is often (but not always under active transcription. g. , expressed as protein.
• Heterochromatin, which consists of mostly inactive DNA. Heterochromatin is a tightly packed form of DNA Its major characteristic is that transcription is limited It seems to serve structural purposes during the chromosomal stages. Heterochromatin can be further distinguished into two types:
  • Constitutive heterochromatin, which is never expressed. It is located around the centromere and usually contains repetitive sequences. In the study of DNA sequences one can distinguish two main types of repeated sequence: Tandem repeats Satellite DNA,
  • Facultative heterochromatin, which is sometimes expressed.

Individual chromosomes cannot be distinguished at this stage - they appear in the nucleus as a homogeneous tangled mix of DNA and protein.

Metaphase chromatin and division

See also: mitosis and meiosis

Human chromosomes during metaphase. Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half Metaphase from the Ancient Greek μετά (after and φάσις (stage is a stage of Mitosis in the eukaryotic Cell cycle in which

In the early stages of mitosis or meiosis (cell division), the chromatin strands become more and more condensed. They cease to function as accessible genetic material (transcription stops) and become a compact transportable form. Transcription is the synthesis of RNA under the direction of DNA This compact form makes the individual chromosomes visible, and they form the classic four arm structure, a pair of sister chromatids attached to each other at the centromere. A chromatid is one of two identical copies of DNA making up a replicated Chromosome, which are joined at their Centromeres for the process of Cell division A centromere is a region of DNA typically found near the middle of a Chromosome where two Sister chromatids come in contact 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). French ( français,) is a Romance language spoken around the world by 118 million people as a native language and by about 180 to 260 million people This is the only natural context in which individual chromosomes are visible with an optical microscope. A microscope ( Greek: ( micron) = small + ( skopein) = to look or see is an instrument for viewing objects that are

During divisions long microtubules attach to the centromere and the two opposite ends of the cell. Microtubules are one of the components of the Cytoskeleton. They have a diameter of 25 nm and length varying from 200 nanometers to 25 micrometers The microtubules then pull the chromatids apart, so that each daughter cell inherits one set of chromatids. Once the cells have divided, the chromatids are uncoiled and can function again as chromatin. In spite of their appearance, chromosomes are structurally highly condensed which enables these giant DNA structures to be contained within a cell nucleus (Fig. 2).

The self assembled microtubules form the spindle, which attaches to chromosomes at specialized structures called kinetochores, one of which is present on each sister chromatid. A chromatid is one of two identical copies of DNA making up a replicated Chromosome, which are joined at their Centromeres for the process of Cell division A special DNA base sequence in the region of the kinetochores provides, along with special proteins, longer-lasting attachment in this region.

Chromosomes in prokaryotes

The prokaryotes - bacteria and archaea - typically have a single circular chromosome, but many variations do exist. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have ^[13] Most bacteria have a single circular chromosome that can range in size from only 160,000 base pairs in the endosymbiotic bacteria Candidatus Carsonella ruddii,^[14] to 12,200,000 base pairs in the soil-dwelling bacteria Sorangium cellulosum. In Molecular biology, two Nucleotides on opposite complementary DNA or RNA strands that are connected via Hydrogen bonds are called An endosymbiont is any Organism that lives within the body or cells of another organism i Candidatus Carsonella ruddii is an endosymbiotic Gamma Proteobacteria; it has the smallest Genome of any characterised bacteria Sorangium cellulosum is a soil-dwelling Gram-negative Bacteria of the group Myxobacteria. ^[15] 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. Spirochaetes is a phylum of distinctive Gram-negative bacteria, which have long helically coiled cells A genus (plural genera from Γένος Latin genus "descent family type gender" is a low-level Taxonomic See also Lyme disease microbiology Borrelia burgdorferi is species of Bacteria of the spirochete class of the Genus Lyme disease, or borreliosis, is an Emerging infectious disease caused by at least three Species of Bacteria belonging to the Genus ^[16]

Structure in sequences

Prokaryotes chromosomes have less sequence-based structure than eukaryotes. Bacteria typically have a single point (the origin of replication) from which replication starts, while some archaea contain multiple replication origins. The Origin of replication (also called the replication origin) is a particular sequence in a Genome at which replication is initiated ^[17] The genes in prokaryotes are often organised in operons, and do not contain introns, unlike eukaryotes. An operon is a functioning unit of key Nucleotide sequences including an operator, a common Promoter, and one or more structural Genes, Introns, derived from the term "intragenic regions" and also called intervening sequence (IVS are DNA regions in a Gene that are not translated into

DNA packaging

Prokaryotes do not possess nuclei, instead their DNA is organized into a structure called the nucleoid. The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other In Prokaryotes, the nucleoid (meaning nucleus-like) is an irregularly-shaped region within the cell of Prokaryotes where the Genetic material ^[18] The nucleoid is a distinct structure and occupies a defined region of the bacterial cell. This structure is however dynamic and is maintained and remodeled by the actions of a range of histone-like proteins, which associate with the bacterial chromosome. ^[19] In archaea, the DNA in chromosomes is even more organized, with the DNA packaged within structures similar to eukaryotic nucleosomes. ^[20][21]

Bacterial chromosomes tend to be tethered to the plasma membrane of the bacteria. The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer 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).

Prokaryotic chromosomes and plasmids are, like eukaryotic DNA, generally supercoiled. The mechanical properties of DNA, which are directly related to its structure are a significant problem for cells. The DNA must first be released into its relaxed state for access for transcription, regulation, and replication. Transcription is the synthesis of RNA under the direction of DNA DNA replication is the process of copying a double-stranded DNA molecule to form two double-stranded molecules

Number of chromosomes in various organisms

Main article: List of number of chromosomes of various organisms

Eukaryotes

These tables give the total number of chromosomes (including sex chromosomes) in a cell nucleus. This page lists the numbers of Chromosomes in various Plants, Animals, Protists, and other living organisms given as the Diploid number For example, human cells are diploid and have 22 different types of autosomes, each present as two copies, and two sex chromosomes. "Haplo" redirects here For the fictional character see The Death Gate Cycle. An autosome is a non-sex Chromosome. It is an ordinarily paired type of chromosome that is the same in both Sexes of a species. A sex-determination system is a biological system that determines the development of sexual characteristics in an Organism. This gives 46 chromosomes in total. Other organisms have more than two copies of their chromosomes, such as Bread wheat which is hexaploid and has six copies of 6 different chromosomes - 42 chromosomes in total. Common wheat, Triticum aestivum, (also known as bread wheat) is a cultivated wheat species

Chromosome numbers in some plants Plant Species # Arabidopsis thaliana (diploid)[22] 10 Rye (diploid)[23] 14 Maize (diploid)[24] 20 Einkorn wheat (diploid)[25] 14 Durum wheat (tetraploid)[25] 28 Bread wheat (hexaploid)[25] 42 Potato (tetraploid)[26] 48 Cultivated tobacco (diploid)[27] 48 Adder's Tongue Fern (diploid)[28] approx 1,440

Chromosome numbers (2n) in some animals Species # Species # Common fruit fly 8 Guinea Pig[29] 64 Dove 16 Garden snail[30] 54 Earthworm Octodrilus complanatus[31] 36 Tibetan fox 36 Domestic cat[32] 38 Domestic pig 38 Lab mouse 40 Lab rat 42 Rabbit 44 Syrian hamster 44 Hare 46 Human[33] 46 Gorillas, Chimpanzees[33] 48 Domestic sheep 54 Elephants[34] 56 Cow 60 Donkey 62 Horse 64 Dog[35] 78 Kingfisher[36] 132 Goldfish[37] 100-104 Silkworm[38] 56

Chromosome numbers in other organisms Species Large Chromosomes Intermediate Chromosomes Small Chromosomes Trypanosoma brucei 11 6 ~100 Chicken[39] 8 2 sex chromosomes 60 Normal members of a particular eukaryotic species all have the same number of nuclear chromosomes (see the table). Arabidopsis thaliana ( A-ra-bi-dóp-sis tha-li-á-na; thale cress, mouse-ear cress or Arabidopsis) is a small Rye ( Secale cereale) is a grass grown extensively as a grain and forage crop Maize (ˈmeɪz ( Zea mays L. ssp mays) known as corn in some countries is a cereal grain domesticated in Mesoamerica Einkorn wheat (from German Einkorn, literally "one grain" can refer either to the wild species of Wheat, Triticum boeoticum (the spelling Durum wheat or macaroni wheat (also spelled Durhum Triticum durum or Triticum turgidum durum) is the only Tetraploid species of Wheat Common wheat, Triticum aestivum, (also known as bread wheat) is a cultivated wheat species The potato is a Starchy Tuberous crop Vegetable from the perennial Solanum tuberosum of the Solanaceae Ophioglossum ( Adder's-tongue) is a genus of about 25-30 species of Ophioglossales in the family Ophioglossaceae, with a Drosophila melanogaster (from the Greek for black-bellied dew-lover) is a two-winged insect that belongs to the Diptera, the order The Guinea pig (also commonly called the cavy after its scientific name Cavia porcellus) is a species of Rodent belonging to the family Caviidae Helix aspersa, Common name the garden snail; has two recent synonyms Cornu aspersum and Cantareus aspersus Earthworm is the usual name for the largest members of Oligochaeta (which is either a class or subclass depending on the author in the phylum Annelida In classical The Tibetan Sand Fox ( Vulpes ferrilata) is Species of true fox endemic to the high Tibetan Plateau in Nepal, WikipediaManual of Style (spelling, articles should conform to one overall spelling style of English typically the one most linked to the article topic (if it is geographic The domestic Pig (or in some areas hog) is normally given the scientific name Sus scrofa scrofa, though some taxonomists use the term The House Mouse ( Mus musculus) is one of the most numerous species of the genus Mus commonly termed a Mouse. Rabbits are small Mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world The Syrian or Golden Hamster, Mesocricetus auratus, is a very well-known member of the Rodent Subfamily Cricetinae, the Hares and jackrabbits are Leporids belonging to the Genus Lepus. Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus Gorillas, the largest of the living Primates are ground-dwelling Herbivores that inhabit the Forests of Africa. Chimpanzee (often shortened to chimp) is the common name for the two extant Species of Apes in the Genus Pan. Elephants ( family: Elephantidae) are large land Mammals of the order Proboscidea. Cattle, colloquially referred to as cows, are domesticated Ungulates a member of the Subfamily Bovinae of the family The donkey or ass, Equus asinus, is a member of the Equidae or horse family and an odd-toed ungulate. The horse ( Equus caballus) is a hoofed ( Ungulate) Mammal, one of eight living species of the family Equidae. The dog ( Canis lupus familiaris) is a domesticated Subspecies of the gray wolf, a Mammal of the Canidae family of the order Kingfishers are small bright colored Birds of the three families Alcedinidae ( River kingfishers, Halcyonidae ( Tree kingfishers, and Cerylidae ( Water The goldfish, Carassius auratus, was one of the earliest Fish to be domesticated, and is still one of the most commonly kept aquarium fish and Trypanosoma brucei is a parasitic Protist species that causes African trypanosomiasis (or Sleeping sickness) in humans and Nagana The chicken ( Gallus gallus, sometimes G gallus domesticus) is a domesticated Fowl which is traditionally believed to have descended from In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. Other eukaryotic chromosomes, i. e. , mitochondrial and plasmid-like small chromosomes, are much more variable in number, and there may be thousands of copies per cell. The 24 human chromosome territories during prometaphase in fibroblast cells. A fibroblast is a type of cell that synthesizes and maintains the Extracellular matrix of many Animal tissues Asexually reproducing species have one set of chromosomes, which is the same in all body cells. Asexual reproduction is a form of reproduction which does not involve Meiosis, Ploidy reduction or Fertilization. Sexually reproducing species have somatic cells (body cells), which are diploid [2n] having two sets of chromosomes, one from the mother and one from the father. The Evolution of sexual reproduction is a major puzzle The first Fossilized evidence of sexually reproducing Organisms is from Eukaryotes of the Stenian Somatic cells are any cells forming the body of an organism as opposed to Germline cells "Haplo" redirects here For the fictional character see The Death Gate Cycle. Gametes, reproductive cells, are haploid [n]: they have one set of chromosomes. A gamete (from Ancient Greek γαμέτης; translated gamete = wife gametes = husband is a cell that fuses with another gamete "Haplo" redirects here For the fictional character see The Death Gate Cycle. Gametes are produced by meiosis of a diploid germ line cell. In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half In Biology and Genetics, the germline of a mature or developing individual is the line (sequence of Germ cells that have genetic material that During meiosis, the matching chromosomes of father and mother can exchange small parts of themselves (crossover), and thus create new chromosomes that are not inherited solely from either parent. When a male and a female gamete merge (fertilization), a new diploid organism is formed. For soil improvement see Fertilization (soil. Some animal and plant species are polyploid [Xn]: they have more than two sets of homologous chromosomes. "Haplo" redirects here For the fictional character see The Death Gate Cycle. Homologous chromosomes are Chromosomes in a Biological cell that pair ( synapse) during Meiosis, or alternatively non-identical chromosomes that Agriculturally important plants such as tobacco or wheat are often polyploid compared to their ancestral species. Tobacco is an Agricultural product recognized as an addictive drug processed from the fresh Leaves of plants in the genus Nicotiana. Wheat ( Triticum spp is a worldwide cultivated grass from the Levant area of the Middle East. Wheat has a haploid number of seven chromosomes, still seen in some cultivars as well as the wild progenitors. A cultivar is a cultivated Plant that has been selected and given a unique name because of its decorative or useful characteristics it is usually distinct from similar The more common pasta and bread wheats are polyploid, having 28 (tetraploid) and 42 (hexaploid) chromosomes compared to the 14 (diploid) chromosomes in the wild wheat. Pasta ( Italian for "dough" is a generic term for Italian variants of Noodles. Bread is a Staple food prepared by Baking a Dough of Flour and Water. [40] Prokaryotes Prokaryote species generally have one copy of each major chromosome, but most cells can easily survive with multiple copies. The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. [41] For example, Buchnera, a symbiont of aphids has multiple copies of its chromosome, ranging from 10–400 copies per cell. This article is about the biological phenomenon for other uses see Symbiosis (disambiguation The term symbiosis (from the Greek [42] However, in some large bacteria, such as Epulopiscium fishelsoni up to 100,000 copies of the chromosome can be present. Epulopiscium fishelsoni ("Fishelson's guest at a fish's banquet" is a Gram-positive bacterium that has a symbiotic relationship [43] Plasmids and plasmid-like small chromosomes are, like in eukaryotes, very variable in copy number. 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, and vice versa. Karyotype Main article: Karyotype Figure 3: Karyogram of a human male In general, the karyotype is the characteristic chromosome complement of a eukaryote species. A karyotype is the characteristic Chromosome complement of a Eukaryote Species. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. [44] The preparation and study of karyotypes is part of cytogenetics. Cytogenetics is a branch of Genetics that is concerned with the study of chromosomes and cell division Although the replication and transcription of DNA is highly standardized in eukaryotes, the same cannot be said for their karotypes, which are often highly variable. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex There may be variation between species in chromosome number and in detailed organization. In some cases there is significant variation within species. Often there is variation 1. between the two sexes. 2. between the germ-line and soma (between gametes and the rest of the body). In Biology and Genetics, the germline of a mature or developing individual is the line (sequence of Germ cells that have genetic material that Soma ( Sanskrit: सोम) or Haoma ( Avestan) from Proto-Indo-Iranian * sauma-, was a ritual drink of importance A gamete (from Ancient Greek γαμέτης; translated gamete = wife gametes = husband is a cell that fuses with another gamete 3. between members of a population, due to balanced genetic polymorphism. Polymorphism in biology occurs when two or more clearly different Phenotypes exist in the same population of a species — in other words the occurrence of more than one 4. geographical variation between races. Allopatric speciation, also known as geographic Speciation, is the phenomenon whereby biological populations are physically isolated by an extrinsic barrier The term race or racial group usually refers to the concept of categorizing Humans into Populations or groups on the basis of various sets 5. mosaics or otherwise abnormal individuals. In Medicine ( Genetics) a mosaic or mosaicism denotes the presence of two populations of cells with different Genotypes in one Finally, variation in karyotype may occur during development from the fertilised egg. The technique of determining the karyotype is usually called karyotyping. Cells can be locked part-way through division (in metaphase) in vitro (in a reaction vial) with colchicine. In vitro ( Latin: within the glass refers to the technique of performing a given experiment in a controlled environment outside of a living Organism Colchicine is a highly poisonous Natural product and Secondary metabolite, originally extracted from plants of the genus Colchicum ( Autumn 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 XY) at the end: Fig. 3. Like many sexually reproducing species, humans have special gonosomes (sex chromosomes, in contrast to autosomes). The XY sex-determination system is the Sex-determination system found in Humans most other Mammals some insects ( Drosophila) and some An autosome is a non-sex Chromosome. It is an ordinarily paired type of chromosome that is the same in both Sexes of a species. These are XX in females and XY in males. Historical note Investigation into the human karyotype took many years to settle the most basic question: how many chromosomes does a normal diploid human cell contain? In 1912, Hans von Winiwarter reported 47 chromosomes in spermatogonia and 48 in oogonia, concluding an XX/XO sex determination mechanism. "Haplo" redirects here For the fictional character see The Death Gate Cycle. A spermatogonium (plural spermatogonia) is an intermediary male Gametogonium (a kind of Germ cell) in the production of Spermatozoa. An oogonium (plural oogonia) is an Immature ovum. It is a female Gametogonium. The X0 sex-determination system is a system that Grasshoppers, Crickets, Cockroaches, and some other Insects use to determine the sex of their A sex-determination system is a biological system that determines the development of sexual characteristics in an Organism. [45] Painter in 1922 was not certain whether the diploid number of man was 46 or 48, at first favouring 46. Theophilus Shickel Painter ( August 22, 1889 &ndash October 5, 1969) was an American zoologist known for his work in identifying [46] He revised his opinion later from 46 to 48, and he correctly insisted on man having an XX/XY system. The XY sex-determination system is the Sex-determination system found in Humans most other Mammals some insects ( Drosophila) and some [47] Considering their techniques, these results were quite remarkable. New techniques were needed to definitively solve the problem: 1. Using cells in culture 2. Pretreating cells in a hypotonic solution, which swells them and spreads the chromosomes 3. Tonicity is a measure of blood capacity or effective osmolality in cell Biology. Arresting mitosis in metaphase by a solution of colchicine 4. Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei Metaphase from the Ancient Greek μετά (after and φάσις (stage is a stage of Mitosis in the eukaryotic Cell cycle in which Colchicine is a highly poisonous Natural product and Secondary metabolite, originally extracted from plants of the genus Colchicum ( Autumn Squashing the preparation on the slide forcing the chromosomes into a single plane 5. Cutting up a photomicrograph and arranging the result into an indisputable karyogram. It took until the mid 1950s until it became generally accepted that the human karyotype included only 46 chromosomes. [48][49] Rather interestingly, chimpanzees (our closest living relatives) have 48 chromosomes. Chromosomal aberrations Main articles: Chromosome abnormalities and aneuploidy The three major single chromosome mutations; deletion (1), duplication (2) and inversion (3). A chromosome abnormality reflects an abnormality of chromosome number or structure Aneuploidy is defined as an abnormal number of Chromosomes Syndromes caused by an extra or missing chromosome are among the most widely recognized Genetic disorders The two major two-chromosome mutations; insertion (1) and translocation (2). In Down syndrome, there are three copies of chromosome 21 Chromosomal aberrations are disruptions in the normal chromosomal content of a cell, and are a major cause of genetic conditions in humans, such as Down syndrome. Down syndrome, Down's syndrome, or trisomy 21 is a Chromosomal disorder caused by the presence of all or part of an extra 21st chromosome. Some chromosome abnormalities do not cause disease in carriers, such as translocations, or chromosomal inversions, although they may lead to a higher chance of having a child with a chromosome disorder. In Genetics, a chromosome translocation is a Chromosome abnormality caused by rearrangement of parts between nonhomologous Chromosomes. An inversion is a Chromosome rearrangement in which a segment of a chromosome is reversed end to end Abnormal numbers of chromosomes or chromosome sets, aneuploidy, may be lethal or give rise to genetic disorders. Aneuploidy is defined as an abnormal number of Chromosomes Syndromes caused by an extra or missing chromosome are among the most widely recognized Genetic disorders Genetic counseling is offered for families that may carry a chromosome rearrangement. Genetic counseling is the process by which patients or relatives at risk of an inherited disorder are advised of the consequences and nature of the disorder the probability of developing The gain or loss of chromosome material can lead to a variety of genetic disorders. A genetic disorder is a condition caused by abnormalities in Genes or Chromosomes While some diseases such as Cancer, are due to genetic abnormalities acquired Human examples include: Cri du chat, which is caused by the deletion of part of the short arm of chromosome 5. Cri du Chat syndrome or Cri-du-Chat syndrome (French for Cry or call of the cat referring to the specific cry of the child also called In Genetics, a deletion (also called gene deletion, deficiency, or deletion mutation) is a Mutation (a genetic aberration "Cri du chat" means "cry of the cat" in French, and the condition was so-named because affected babies make high-pitched cries that sound like a cat. Affected individuals have wide-set eyes, a small head and jaw and are moderately to severely mentally retarded and very short. Wolf-Hirschhorn syndrome, which is caused by partial deletion of the short arm of chromosome 4. It is characterized by severe growth retardation and severe to profound mental retardation. Down's syndrome, usually is caused by an extra copy of chromosome 21 (trisomy 21). Down syndrome, Down's syndrome, or trisomy 21 is a Chromosomal disorder caused by the presence of all or part of an extra 21st chromosome. Down syndrome, Down's syndrome, or trisomy 21 is a Chromosomal disorder caused by the presence of all or part of an extra 21st chromosome. Characteristics include decreased muscle tone, stockier build, asymmetrical skull, slanting eyes and mild to moderate mental retardation. [50] Edwards syndrome, which is the second most common trisomy after Down syndrome. Trisomy 18 or Edwards Syndrome is a Genetic disorder caused by the presence of all or part of an extra 18th chromosome. It is a trisomy of chromosome 18. Symptoms include mental and motor retardation and numerous congenital anomalies causing serious health problems. Ninety percent die in infancy; however, those who live past their first birthday usually are quite healthy thereafter. They have a characteristic hand appearance with clenched hands and overlapping fingers. Patau Syndrome, also called D-Syndrome or trisomy-13. Patau syndrome, also known as trisomy 13, is a chromosomal abnormality a Syndrome in which a patient has an additional chromosome 13 due Symptoms are somewhat similar to those of trisomy-18, but they do not have the characteristic hand shape. Idic15, abbreviation for Isodicentric 15 on chromosome 15; also called the following names due to various researches, but they all mean the same; IDIC(15), Inverted dupliction 15, extra Marker, Inv dup 15, partial tetrasomy 15 Jacobsen syndrome, also called the terminal 11q deletion disorder. Isodicentric 15, or idic(15, is a chromosome abnormality in which a child is born with extra genetic material from chromosome 15. Jacobsen Syndrome, also known as 11q deletion, is a rare Congenital disorder resulting from deletion of a terminal region of Chromosome 11 that includes [1] This is a very rare disorder. Those affected have normal intelligence or mild mental retardation, with poor expressive language skills. Most have a bleeding disorder called Paris-Trousseau syndrome. Klinefelter's syndrome (XXY). Klinefelter's syndrome, 47XXY or XXY syndrome is a condition caused by a Chromosome Aneuploidy. Men with Klinefelter syndrome are usually sterile, and tend to have longer arms and legs and to be taller than their peers. Boys with the syndrome are often shy and quiet, and have a higher incidence of speech delay and dyslexia. Dyslexia is considered to be a Learning disability. It manifests primarily as a difficulty with written language particularly with Reading and Spelling During puberty, without testosterone treatment, some of them may develop gynecomastia. Gynecomastia, or gynaecomastia, ˌgaɪnəkoʊˈmæstiə is the development of abnormally large Mammary glands in Males resulting in breast enlargement which Turner syndrome (X instead of XX or XY). Turner syndrome or Ullrich-Turner syndrome encompasses several conditions of which monosomy X is the most common In Turner syndrome, female sexual characteristics are present but underdeveloped. People with Turner syndrome often have a short stature, low hairline, abnormal eye features and bone development and a "caved-in" appearance to the chest. XYY syndrome. XYY syndrome is an Aneuploidy of the Sex chromosomes in which a Human Male receives an extra Y chromosome, producing a 47XYY XYY boys are usually taller than their siblings. Like XXY boys and XXX girls, they are somewhat more likely to have learning difficulties. Triple-X syndrome (XXX). Triple X syndrome is a form of chromosomal variation characterized by the presence of an extra X chromosome in each cell of a human female XXX girls tend to be tall and thin. They have a higher incidence of dyslexia. Small supernumerary marker chromosome. Humans typically have 22 pairs of autosomal Chromosomes in our cells, and a pair of Sex chromosomes About 2 This means there is an extra, abnormal chromosome. Features depend on the origin of the extra genetic material. Cat-eye syndrome and isodicentric chromosome 15 syndrome (or Idic15) are both caused by a supernumerary marker chromosome, as is Pallister-Killian syndrome. Trisomy 22 Cat Eye Syndrome is a very rare malformation involving Chromosome 22. Isodicentric 15, or idic(15, is a chromosome abnormality in which a child is born with extra genetic material from chromosome 15. Pallister-Killian syndrome (also tetrasomy 12p mosaicism or Pallister mosaic aneuploidy syndrome) is an extremely rare Genetic disorder occurring in Chromosomal mutations produce changes in whole chromosomes (more than one gene) or in the number of chromosomes present. Deletion - loss of part of a chromosome Duplication - extra copies of a part of a chromosome Inversion - reverse the direction of a part of a chromosome Translocation - part of a chromosome breaks off and attaches to another chromosome Most mutations are neutral - have little or no effect A detailed graphical display of all human chromosomes and the diseases annotated at the correct spot may be found at [2]. Human chromosomes Human cells have 23 pairs of large linear nuclear chromosomes, giving a total of 46 per cell. In addition to these, human cells have many hundreds of copies of the mitochondrial genome. The mitochondrial genome is the genetic material of the Mitochondria. Sequencing of the human genome has provided a great deal of information about each of the chromosomes. The term DNA sequencing encompasses biochemical methods for determining the order of the Nucleotide bases Adenine, Guanine, Cytosine 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. The Wellcome Trust Sanger Institute (formerly the Sanger Centre is a Genome research centre in the Wellcome Trust Genome Campus in Cambridgeshire, [51] Number of genes is an estimate as it is in part based on gene predictions. Gene finding typically refers to the area of Computational biology that is concerned with algorithmically identifying stretches of sequence usually genomic DNA Total chromosome length is an estimate as well, based on the estimated size of unsequenced heterochromatin regions. Heterochromatin is a tightly packed form of DNA Its major characteristic is that transcription is limited Chromosome Genes Total bases Sequenced bases[52] 1 3,148 247,200,000 224,999,719 2 902 242,750,000 237,712,649 3 1,436 199,450,000 194,704,827 4 453 191,260,000 187,297,063 5 609 180,840,000 177,702,766 6 1,585 170,900,000 167,273,992 7 1,824 158,820,000 154,952,424 8 781 146,270,000 142,612,826 9 1,229 140,440,000 120,312,298 10 1,312 135,370,000 131,624,737 11 405 134,450,000 131,130,853 12 1,330 132,290,000 130,303,534 13 623 114,130,000 95,559,980 14 886 106,360,000 88,290,585 15 676 100,340,000 81,341,915 16 898 88,820,000 78,884,754 17 1,367 78,650,000 77,800,220 18 365 76,120,000 74,656,155 19 1,553 63,810,000 55,785,651 20 816 62,440,000 59,505,254 21 446 46,940,000 34,171,998 22 595 49,530,000 34,893,953 X (sex chromosome) 1,093 154,910,000 151,058,754 Y (sex chromosome) 125 57,740,000 22,429,293 See also Locus (explains gene location nomenclature) Sex-determination system XY sex-determination system X chromosome X-inactivation Y chromosome Y-chromosomal Adam Y-chromosomal Aaron Genetic genealogy Genealogical DNA test Genetic deletion List of number of chromosomes of various organisms External links What Can Our Chromosomes Tell Us?,an accessible and comprehensive look at chromosomes, from the University of Utah's Genetic Science Learning Center Try making a karyotype yourself, from the University of Utah's Genetic Science Learning Center Kimballs Chromosome pages Chromosome News from Genome News Network Eurochromnet, European network for Rare Chromosome Disorders on the Internet http://www.ensembl.org Ensembl project, presenting chromosomes, their genes and syntenic loci graphically via the web [Genographic Project] http://ghr.nlm.nih.gov/ghr/chromosomes References ^ Nägeli C. History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance Structure The "skeleton" of adenine Chromosome 1 is the designation for the largest Human Chromosome. Chromosome 2 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome 125px|right Chromosome 3 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 4 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 5 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 6 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 7 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 8 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 9 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 10 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 11 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 12 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 13 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 14 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 15 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 16 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 17 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 18 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 19 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 20 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 21 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Chromosome 22 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of Chromosome 22 The X chromosome is one of the two sex-determining Chromosomes in many animal species including mammals (the other is the Y chromosome) The Y chromosome is the sex-determining Chromosome in most Mammals including Humans In mammals it contains the gene SRY, which triggers In the fields of Genetics and Evolutionary computation, a locus (plural loci) is a fixed position on a Chromosome such as the position of a A sex-determination system is a biological system that determines the development of sexual characteristics in an Organism. The XY sex-determination system is the Sex-determination system found in Humans most other Mammals some insects ( Drosophila) and some The X chromosome is one of the two sex-determining Chromosomes in many animal species including mammals (the other is the Y chromosome) X-inactivation (also called lyonization) is a process by which one of the two copies of the X chromosome present in Female Mammals is inactivated The Y chromosome is the sex-determining Chromosome in most Mammals including Humans In mammals it contains the gene SRY, which triggers In human Genetics, Y-chromosomal Adam ( Y- MRCA) is the patrilineal Human Most recent common ancestor (MRCA from whom all Y-chromosomal Aaron is the name given to the hypothesised most recent common ancestor of many of the patrilineal Jewish priestly caste known as Kohanim Genetic genealogy is the application of Genetics to traditional genealogy. A genealogical DNA test examines the Nucleotides at specific locations on a person's DNA for Genetic genealogy purposes In Genetics, a deletion (also called gene deletion, deficiency, or deletion mutation) is a Mutation (a genetic aberration This page lists the numbers of Chromosomes in various Plants, Animals, Protists, and other living organisms given as the Diploid number Ensembl is a joint scientific project between the European Bioinformatics Institute and the Wellcome Trust Sanger Institute, which was launched in 1999 in response to the imminent History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance In Classical genetics, synteny describes the physical co-localization of genetic loci on the same Chromosome within an individual or Species 1842. Zur Entwickelungsgeschichte des Pollens bei den Phanerogamen. Ovell & Füssli, Zürich. ^ Harris H. 1999. The birth of the cell. 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ISBN 0-13-436265-9.   ^ http://vega.sanger.ac.uk/Homo_sapiens/index.html All data in this table was derived from this database, July 7 2007. ^ Sequenced percentages are based on fraction of euchromatin portion, as the Human Genome Project goals called for determination of only the euchromatic portion of the genome. The Human Genome Project (HGP was an international Scientific research project with a primary goal to determine the sequence of chemical base pairs which make up DNA Euchromatin is a lightly packed form of Chromatin that is rich in Gene concentration and is often (but not always under active transcription. Telomeres, centromeres, and other heterochromatic regions have been left undetermined, as have a small number of unclonable gaps. A telomere is a region of repetitive DNA at the end of Chromosomes which protects the end of the chromosome from destruction A centromere is a region of DNA typically found near the middle of a Chromosome where two Sister chromatids come in contact Heterochromatin is a tightly packed form of DNA Its major characteristic is that transcription is limited See http://www.ncbi.nlm.nih.gov/genome/seq/ for more information on the Human Genome Project.