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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.
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]
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]
In about 1 to 2% of persons of Down syndrome, mosaicism is seen — that is when some of the cells have 46 chromosomes (two No. 21 chromosomes) and some cells have 47 chromosomes (three No. 21 ...
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]
It consists of 22 autosomes plus one copy of the X chromosome and one copy of the Y chromosome. It contains approximately 3.1 billion base pairs (3.1 Gb or 3.1 x 10 9 bp). [ 6 ] This represents the size of a composite genome based on data from multiple individuals but it is a good indication of the typical amount of DNA in a haploid set of ...
Turner syndrome results from a single X chromosome (45,X or 45,X0). Klinefelter syndrome, the most common male chromosomal disease, otherwise known as 47,XXY, is caused by an extra X chromosome. Edwards syndrome is caused by trisomy (three copies) of chromosome 18. Down syndrome, a common chromosomal disease, is caused by trisomy of chromosome 21.