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The extra chromosome content can arise through several different ways. The most common cause (about 92–95% of cases) is a complete extra copy of chromosome 21, resulting in trisomy 21. [91] [96] In 1–2.5% of cases, some of the cells in the body are normal and others have trisomy 21, known as mosaic Down syndrome.
Cat-eye syndrome (CES) or Schmid–Fraccaro syndrome is a rare condition caused by an abnormal extra chromosome, i.e. a small supernumerary marker chromosome. [2] This chromosome consists of the entire short arm and a small section of the long arm of chromosome 22. In consequence, individuals with the cat-eye syndrome have three (trisomic) or ...
Trisomy X, also known as triple X syndrome and characterized by the karyotype [note 1] 47,XXX, is a chromosome disorder in which a female has an extra copy of the X chromosome. It is relatively common and occurs in 1 in 1,000 females, but is rarely diagnosed; fewer than 10% of those with the condition know they have it.
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 ...
Karyotype of a human with Trisomy 21 (Down syndrome). Trisomies can occur with any chromosome, but often result in miscarriage rather than live birth.For example, Trisomy 16 is most common in human pregnancies, occurring in more than 1%, but the only surviving embryos are those having some normal cells in addition to the trisomic cells (mosaic trisomy 16). [3]
Patau syndrome. Patau syndrome is a syndrome caused by a chromosomal abnormality, in which some or all of the cells of the body contain extra genetic material from chromosome 13. The extra genetic material disrupts normal development, causing multiple and complex organ defects. This can occur either because each cell contains a full extra copy ...
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 ...
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.