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Chromosome 21 from Human Genome Program Normal human Karyotype. Down syndrome is a chromosomal abnormality characterized by the presence of an extra copy of genetic material on chromosome 21, either in whole (trisomy 21) or part (such as due to translocations). The effects of the extra copy varies greatly from individual to individual ...
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. [92] [97] 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.
A karyotype of somebody affected with Down syndrome, depicting the presence of a full additional copy of chromosome 21. The presence of this extra copy is also referred to as Trisomy 21. The following conditions are caused by changes in the structure or number of copies of chromosome 21: Cancers: Rearrangements (translocations) of genetic ...
The presence of an extra chromosome 21, which is found in Down syndrome, is called trisomy 21. Trisomy 18 and Trisomy 13, known as Edwards syndrome and Patau syndrome, respectively, are the two other autosomal trisomies recognized in live-born humans. Trisomy of the sex chromosomes is also possible, for example , , and . 4/5
Trisomy 21, an extra copy of the 21st chromosome, is responsible for causing Down syndrome, and the mouse chromosome 16 closely resembles human chromosome 21. [1] In 1979, trisomy of the mouse chromosome 16 (Ts16) initially showed potential to be a model organism for human Down syndrome. [2]
Trisomies are sometimes characterised as "autosomal trisomies" (trisomies of the non-sex chromosomes) and "sex-chromosome trisomies." Autosomal trisomies are described by referencing the specific chromosome that has an extra copy. [citation needed] Thus, for example, the presence of an extra chromosome 21, which is found in Down syndrome, is ...
Rather than having monosomy, or only one copy, the majority of aneuploid people have trisomy, or three copies of one chromosome. [citation needed] An example of trisomy in humans is Down syndrome, which is a developmental disorder caused by an extra copy of chromosome 21; the disorder is therefore also called "trisomy 21". [7]
A chromosomal disorder is a missing, extra, or irregular portion of chromosomal DNA. [33] It can be from an atypical number of chromosomes or a structural abnormality in one or more chromosomes. An example of these disorders is Trisomy 21 (the most common form of Down syndrome), in which there is an extra copy of chromosome 21 in all cells. [34]