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The extra chromosome 21 material that causes Down syndrome may be due to a Robertsonian translocation. The long arm of chromosome 21 is attached to the long arm of another chromosome, often chromosome 14 [46,XX,t(14;21)] or itself [called an isochromosome , 45,XX,t(21;21)(q10;q10)] as seen in the translocation karyotype figure.
Down syndrome or Down's syndrome, [12] also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. [3] It is usually associated with developmental delays, mild to moderate intellectual disability , and characteristic physical features.
Research of Down syndrome–related genes is based on studying the genes located on chromosome 21. In general, this leads to an overexpression of the genes. [1] [2] Understanding the genes involved may help to target medical treatment to individuals with Down syndrome. It is estimated that chromosome 21 contains 200 to 250 genes. [3]
When there is an extra chromosome 21, the result is Down syndrome. There are three genetic variations of Down syndrome: Trisomy 21: This occurs when there is a third copy of chromosome 21. This is ...
Down syndrome: 1:600 Chromosome 21 Klinefelter syndrome: 1:500–1000 males Additional X chromosome Turner syndrome: 1:2000 females Loss of X chromosome Sickle cell anemia: 1 in 50 births in parts of Africa; rarer elsewhere β-globin (on chromosome 11) Bloom syndrome: 1:48000 Ashkenazi Jews BLM Cancers Breast/Ovarian cancer (susceptibility)
It shows 22 homologous autosomal chromosome pairs, both the female (XX) and male (XY) versions of the two sex chromosomes, as well as the mitochondrial genome (at bottom left). In genetics, a chromosomal rearrangement is a mutation that is a type of chromosome abnormality involving a change in the structure of the native chromosome. [1]
“In the most common type of Down syndrome, there are 47 chromosomes, with the extra one being chromosome 21 — so the patient has three No. 21 chromosomes in all the cells of their body.
Trisomy 21 – Down syndrome, an example of a polysomy at chromosome 21. Polysomy is a condition found in many species, including fungi, plants, insects, and mammals, in which an organism has at least one more chromosome than normal, i.e., there may be three or more copies of the chromosome rather than the expected two copies. [1]