Search results
Results From The WOW.Com Content Network
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.
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]
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.
Chromosome or gene involved Chromosomal conditions 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 ...
Chromosome 21 is both the smallest human autosome and chromosome, [4] with 46.7 million base pairs (the building material of DNA) representing about 1.5 percent of the total DNA in cells. Most people have two copies of chromosome 21, while those with three copies of chromosome 21 (trisomy 21) have Down syndrome.
“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.
46,XX/46,XY chimeric or mosaic is associated with a wide spectrum of different physical presentations, with cases ranging from having a completely normal male or female phenotype [7] [8] [9] to some cases having ovotesticular syndrome. Due to this variation, genetic testing is the only way to reliably make a diagnosis.