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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.
The trisomy 21 karyotype figure shows the chromosomal arrangement, with the prominent extra chromosome 21. Trisomy 21 is the cause of approximately 95% of observed Down syndrome, with 88% coming from nondisjunction in the maternal gamete and 8% coming from nondisjunction in the paternal gamete. [4]
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.
Trisomy 21, one of the three types of Down syndrome, indicates that an individual has a duplicate of chromosome 21. The extra chromosome changes how one’s brain and body develop, and can lead to ...
This is a list of people with Down syndrome, a condition also known as Down's syndrome or trisomy 21. Down syndrome is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. [1] It is typically associated with developmental delays, characteristic physical features, and mild to moderate intellectual disability ...
The clinical name for Down syndrome is trisomy 21, a condition in which a person is born with an extra chromosome, causing mild to moderate cognitive disability, developmental delays and physical ...
The chromosomal conditions trisomy 9 and trisomy 21 (Down syndrome) can cause the palpebral fissures to be upslanted, [2] whereas Marfan syndrome can cause a downslant. [3] An increase in vertical height can be seen in genetic disorders such as cri-du-chat syndrome .
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