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Encyclopedia > Chromosome 21 (human)

Chromosome 21 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 21 is the smallest human chromosome, spanning almost 47 million nucleotides (the building material of DNA) and representing about 1.5 percent of the total DNA in cells. Figure 1: A representation of a condensed eukaryotic chromosome, as seen during cell division. ... Trinomial name Homo sapiens sapiens Linnaeus, 1758 Humans, or human beings, are bipedal primates belonging to the mammalian species Homo sapiens (Latin for wise man or knowing man) under the family Hominidae (the great apes). ... A nucleotide is a chemical compound that consists of a heterocyclic base, a sugar, and one or more phosphate groups. ... The structure of part of a DNA double helix. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell. Cells in culture, stained for keratin (red) and DNA (green). ...


In 2000, researchers working on the Human Genome Project announced that they had determined the sequence of base pairs that make up this chromosome. Chromosome 21 was the second human chromosome to be fully sequenced. This article is about the year 2000. ... The Human Genome Project is a project to code the 3 billion Genes contained in the human genome and to identify all the genes present in it. ...


Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 21 likely contains between 200 and 400 genes. For other meanings of this term, see gene (disambiguation). ...

Contents

Genes

The following are some of the genes located on chromosome 21:

  • APP: amyloid beta (A4) precursor protein (peptidase nexin-II, Alzheimer disease)
  • CBS: cystathionine-beta-synthase
  • CLDN14: claudin 14
  • HLCS: holocarboxylase synthetase (biotin-(proprionyl-Coenzyme A-carboxylase (ATP-hydrolysing)) ligase)
  • KCNE1: potassium voltage-gated channel, Isk-related family, member 1
  • KCNE2: potassium voltage-gated channel, Isk-related family, member 2
  • LAD: leukocyte adhesion deficiency (symbols are ITGB2, CD18, LCAMB)
  • SOD1: superoxide dismutase 1, soluble (amyotrophic lateral sclerosis 1 (adult))
  • TMPRSS3: transmembrane protease, serine 3

HLCS (holocarboxylase synthetase (biotin-(proprionyl-Coenzyme A-carboxylase (ATP-hydrolysing)) ligase)) is a human gene that provides instructions for making an enzyme called holocarboxylase synthetase (EC 6. ... KCNE1 is a gene associated with Long QT syndrome type 5. ...

Diseases

The following diseases are some of those related to genes on chromosome 21:

Amyotrophic lateral sclerosis (ALS, sometimes called Lou Gehrig’s disease, Maladie de Charcot or motor neurone disease) is a progressive, fatal neurodegenerative disease caused by the degeneration of motor neurons. ... Holocarboxylase synthetase deficiency is an inherited disorder in which the body is unable to use the vitamin biotin effectively. ... Homocystinuria, also known as Cystathionine beta synthase deficiency, is inherited disorder of the metabolism of the amino acid methionine. ... Jervell and Lange-Nielsen syndrome is a condition that causes profound hearing loss and arrhythmia, it is a type of long QT syndrome. ... Leukocyte adhesion deficiency (abbreviated LAD), is a rare autosomal recessive disorder characterized by immunodeficiency resulting in recurrent infections. ... Nonsyndromic deafness is hearing loss that is not associated with other signs and symptoms. ... Romano-Ward syndrome, is the major variant of long QT syndrome. ...

Chromosomal conditions

The following conditions are caused by changes in the structure or number of copies of chromosome 21:

  • Cancers: Rearrangements (translocations) of genetic material between chromosome 21 and other chromosomes have been associated with several types of cancer. For example, acute lymphoblastic leukemia (a type of blood cancer most often diagnosed in childhood) has been associated with a translocation between chromosomes 12 and 21. Another form of leukemia, acute myeloid leukemia, has been associated with a translocation between chromosomes 8 and 21.

In a small percentage of cases, Down syndrome is caused by a rearrangement of chromosomal material between chromosome 21 and another chromosome. As a result, a person has the usual two copies of chromosome 21, plus extra material from chromosome 21 attached to another chromosome. These cases are called translocation Down syndrome. Researchers believe that extra copies of genes on chromosome 21 disrupt the course of normal development, causing the characteristic features of Down syndrome and the increased risk of medical problems associated with this disorder. Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these cells to invade other tissues, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis. ... Chromosomal translocation of the 4th and 20th chromosome. ... Acute lymphoblastic leukemia (ALL), also known as acute lymphocytic leukemia, is a cancer of the white blood cells, characterised by the overproduction and continuous multiplication of malignant and immature white blood cells (referred to as lymphoblasts) in the bone marrow. ... Acute myeloid leukemia (AML), which is also known as acute myelogenous leukemia, is a cancer of the myeloid line of white blood cells, characterized by the rapid proliferation of abnormal cells which accumulate in the bone marrow and interfere with the production of normal blood cells. ...

  • Other changes in the number or structure of chromosome 21 can have a variety of effects, including mental retardation, delayed development, and characteristic facial features. In some cases, the signs and symptoms are similar to those of Down syndrome. Changes to chromosome 21 include a missing segment of the chromosome in each cell (partial monosomy 21) and a circular structure called ring chromosome 21. A ring chromosome occurs when both ends of a broken chromosome are reunited.
  • Duplication in Amyloid precursor protein (APP) locus (duplicated segment varies in length but includes APP) on Chromosome 21 was found to cause early onset familial Alzheimer's disease (AD) in a french family set (Rovelet-Lecrux et al) and a dutch family set (Sleegers et al). Compared to AD caused by missense mutations in APP, the frequency of the AD caused by APP duplications is significant. ALL the patients that have an extra copy of APP gene due to the locus duplication show AD with severe Cerebral amyloid angiopathy (CAA).

Mental retardation is a term for a pattern of persistently slow learning of basic motor and language skills (milestones) during childhood, and a significantly below-normal global intellectual capacity as an adult. ... Amyloid beta (Aβ or Abeta) is a protein fragment on 39-42 amino acids that is the main constituent of amyloid plaques in various neurological disorders, most prominently Alzheimers disease. ... Congophilic angiopathy is a condition in which the same amyloid protein associated with Alzheimers disease (Amyloid beta) is deposited in the walls of the blood vessels of the brain. ...

References

  • Antonarakis SE, Lyle R, Dermitzakis ET, Reymond A, Deutsch S (2004). "Chromosome 21 and down syndrome: from genomics to pathophysiology". Nat Rev Genet 5 (10): 725-38. PMID 15510164.
  • Antonarakis SE, Lyle R, Deutsch S, Reymond A (2002). "Chromosome 21: a small land of fascinating disorders with unknown pathophysiology". Int J Dev Biol 46 (1): 89-96. PMID 11902692.
  • Antonarakis SE (2001). "Chromosome 21: from sequence to applications". Curr Opin Genet Dev 11 (3): 241-6. PMID 11377958.
  • Gardiner K, Davisson M (2000). "The sequence of human chromosome 21 and implications for research into Down syndrome". Genome Biol 1 (2): REVIEWS0002. PMID 11178230.
  • Gilbert F (1997). "Disease genes and chromosomes: disease maps of the human genome. Chromosome 21". Genet Test 1 (4): 301-6. PMID 10464663.
  • Hattori M, Fujiyama A, Taylor TD, Watanabe H, Yada T, Park HS, Toyoda A, Ishii K, Totoki Y, Choi DK, Groner Y, Soeda E, Ohki M, Takagi T, Sakaki Y, Taudien S, Blechschmidt K, Polley A, Menzel U, Delabar J, Kumpf K, Lehmann R, Patterson D, Reichwald K, Rump A, Schillhabel M, Schudy A, Zimmermann W, Rosenthal A, Kudoh J, Schibuya K, Kawasaki K, Asakawa S, Shintani A, Sasaki T, Nagamine K, Mitsuyama S, Antonarakis SE, Minoshima S, Shimizu N, Nordsiek G, Hornischer K, Brant P, Scharfe M, Schon O, Desario A, Reichelt J, Kauer G, Blocker H, Ramser J, Beck A, Klages S, Hennig S, Riesselmann L, Dagand E, Haaf T, Wehrmeyer S, Borzym K, Gardiner K, Nizetic D, Francis F, Lehrach H, Reinhardt R, Yaspo ML (2000). "The DNA sequence of human chromosome 21". Nature 405 (6784): 311-9. PMID 10830953.
  • Sawinska M, Ladon D (2004). "Mechanism, detection and clinical significance of the reciprocal translocation t(12;21)(p12;q22) in the children suffering from acute lymphoblastic leukaemia". Leuk Res 28 (1): 35-42. PMID 14630078.
  • Sleegers K,Brouwers N,Gijselinck I,Theuns J, Goossens D, Wauters J,Del-Favero J,Cruts M, van Duijn CM,Van Broeckhoven C. (2006). "APP duplication is sufficient to cause early onset Alzheimer's dementia with cerebral amyloid angiopathy". Brain. PMID 16921174.
  • Rovelet-Lecrux A,Hannequin D,Raux G,Le Meur N,Laquerriere A, Vital A,Dumanchin C,Feuillette S,Brice A,Vercelletto M, Dubas F,Frebourg T,Campion D. (2005). "APP locus duplication causes autosomal dominant early-onset Alzheimer disease with cerebral amyloid angiopathy". Nature Genetics. PMID 16369530.
Human chromosomes

{1} {2} {3} {4} {5} {6} {7} {8} {9} {10} {11} {12} {13} {14} {15} {16} {17} {18} {19} {20} {21} {22} {X} {Y} The human genome is the genome of Homo sapiens. ... Chromosome 1 is, by convention, the designation for the largest human chromosome. ... Chromosome 2 is one of the 23 pairs of chromosomes in humans. ... Chromosome 3 is one of the 23 pairs of chromosomes in humans. ... Chromosome 4 is one of the 23 pairs of chromosomes in humans. ... Chromosome 5 is one of the 23 pairs of chromosomes in humans. ... Chromosome 6 is one of the 23 pairs of chromosomes in humans. ... Chromosome 7 is one of the 23 pairs of chromosomes in humans. ... Chromosome 8 is one of the 23 pairs of chromosomes in humans. ... Chromosome 9 is one of the 23 pairs of chromosomes in humans. ... Chromosome 10 is one of the 23 pairs of chromosomes in humans. ... Chromosome 11 is one of the 23 pairs of chromosomes in humans. ... Chromosome 12 is one of the 23 pairs of chromosomes in humans. ... Chromosome 13 is one of the 23 pairs of chromosomes in humans. ... Chromosome 14 is one of the 23 pairs of chromosomes in humans. ... Chromosome 15 is one of the 23 pairs of chromosomes in humans. ... Chromosome 16 is one of the 23 pairs of chromosomes in humans. ... Chromosome 17 is one of the 23 pairs of chromosomes in humans. ... Chromosome 18 is one of the 23 pairs of chromosomes in humans. ... Chromosome 19 is one of the 23 pairs of chromosomes in humans. ... Chromosome 20 is one of the 23 pairs of chromosomes in humans. ... Chromosome 22 is one of the 23 pairs of chromosomes in humans. ... The X chromosome is one of the two sex-determining chromosomes in many animal species, including mammals (the other is the Y chromosome). ... The human Y chromosome is one of two sex chromosomes, it contains the genes that cause testis development, thus determining maleness. ...

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  Results from FactBites:
 
Facts About Down Syndrome (3817 words)
This condition, in which three copies of chromosome 21 are present in all cells of the individual, is called trisomy 21.
If the resulting sperm or ovum receives a chromosome 14 (or another chromosome), with a piece of chromosome 21 attached and retains the chromosome 21 that lost a section due to translocation, then the reproductive cells contain the normal or balanced amount of chromosome 21.
In 88% of cases, the extra copy of chromosome 21 is derived from the mother.
Chromosome 21 - Genetics Home Reference (787 words)
Chromosome 21 is one of the 23 pairs of chromosomes in humans.
Genes on chromosome 21 are among the estimated 20,000 to 25,000 total genes in the human genome.
Changes to chromosome 21 include a missing segment of the chromosome in each cell (partial monosomy 21) and a circular structure called ring chromosome 21 that is caused by the breakage and reunion of both ends of the chromosome.
  More results at FactBites »

 
 

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