Chromosome 21 is one of the 23 pairs of chromosomes in humans. A chromosome is an organized structure of DNA and Protein that is found in cells. Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus People normally have two copies of this chromosome. The trisomy of the 21 causes Down Syndrome. A trisomy is a form of Aneuploidy with the presence of three copies instead of the normal two of a particular 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. Chromosome 21 is the smallest human chromosome, spanning almost 47 million nucleotides (the building material of DNA) and representing about 1. Nucleotides are Organic compounds that consist of three joined structures a nitrogenous base a Sugar, and a Phosphate group Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known 5 percent of the total DNA in cells. 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
In 2000, researchers working on the Human Genome Project announced that they had determined the sequence of base pairs that make up this chromosome. 2000 ( MM) was a Leap year that started on Saturday of the Common Era, in accordance with the Gregorian calendar. 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 Chromosome 21 was the second human chromosome to be fully sequenced.
Identifying genes on each chromosome is an active area of genetic research. History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance 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.
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
- PCNT: centrosomal pericentrin
Diseases & disorders
The following diseases are some of those related to genes on chromosome 21:
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. Amyloid precursor protein (APP is an Integral membrane protein Cystathionine-beta-synthase, also known as CBS, is a human Gene. Claudin 14, also known as CLDN14, is a human Gene. It belongs to the group of Claudins HLCS ( holocarboxylase synthetase (biotin-(proprionyl-Coenzyme A-carboxylase (ATP-hydrolysing ligase) is a Human Gene that provides instructions for making Potassium voltage-gated channel Isk-related family member 1, also known as KCNE1, is a human Gene. KCNE2, also known as potassium voltage-gated channel Isk-related family member 2, is a human Gene. Integrin beta 2 (complement component 3 receptor 3 and 4 subunit, also known as CD18 or ITGB2, is a human Gene. Superoxide dismutase 1 soluble (amyotrophic lateral sclerosis 1 (adult, also known as SOD1, is a human protein and Gene. Transmembrane protease serine 3, also known as TMPRSS3, is a human Gene. Pericentrin (kendrin, also known as PCNT, is a human Gene. Alzheimer's disease ( AD) also called Alzheimer disease or simply Alzheimer's, is the most common form of Dementia. Amyotrophic Lateral Sclerosis ( ALS, sometimes called Maladie de Charcot, or in the United States Lou Gehrig's Disease) is a progressive 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. Holocarboxylase synthetase deficiency is an inherited Metabolic disorder in which the body is unable to use the Vitamin Biotin effectively Homocystinuria, also known as Cystathionine beta synthase deficiency, is an inherited disorder of the Metabolism of the Amino acid Methionine Jervell and Lange-Nielsen syndrome, a type of Long QT syndrome, causes the Cardiac muscle to take longer than usual to recharge between beats 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. Majewski osteodysplastic primordial dwarfism type II is a rare genetic disorder causing Dwarfism. Cancer (medical term Malignant Neoplasm) is a class of Diseases in which a group of cells display uncontrolled In Genetics, a chromosome translocation is a Chromosome abnormality caused by rearrangement of parts between nonhomologous Chromosomes. 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. Acute lymphoblastic leukemia ( ALL) is a form of Leukemia, or cancer of the white blood cells. Another form of leukemia, acute myeloid leukemia, has been associated with a translocation between chromosomes 8 and 21. Acute myeloid leukemia ( AML) also known as acute myelogenous leukemia, is a Cancer of the Myeloid line of White blood cells characterized
In a small percentage of cases, Down syndrome is caused by a rearrangement of chromosomal material between chromosome 21 and another 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. 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.
- 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. Mental retardation is a generalized triarchic disorder characterized by subaverage cognitive functioning and deficits in two or more adaptive behaviors with onset before the age 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). Amyloid precursor protein (APP is an Integral membrane protein Alzheimer's disease ( AD) also called Alzheimer disease or simply Alzheimer's, is the most common form of Dementia. 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). Cerebral amyloid angiopathy, also known as congophilic angiopathy, is a form of Angiopathy in which Amyloid deposits in the walls of the blood
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