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Turner syndrome is the only full monosomy that is seen in humans — all other cases of full monosomy are lethal and the individual will not survive development. Cri du chat syndrome – (French for "cry of the cat" after the persons' malformed larynx) a partial monosomy caused by a deletion of the end of the short arm of chromosome 5
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".
The terms "partial monosomy" and "partial trisomy" are used to describe an imbalance of genetic material caused by loss or gain of part of a chromosome. In particular, these terms would be used in the situation of an unbalanced translocation , where an individual carries a derivative chromosome formed through the breakage and fusion of two ...
2p15-16.1 microdeletion is an extremely rare genetic disorder caused by a small deletion in the short arm of human chromosome 2. First described in two patients in 2007, [1] by 2013 only 21 [citation needed] people have been reported as having the disorder in the medical literature. [2] [3] [4] [5]
The disorder arises from the deletion of part of the small arm of chromosome 17p (which includes both the LIS1 and 14-3-3 epsilon genes), leading to partial monosomy. There may be unbalanced translocations (e.g., 17q:17p or 12q:17p), or the presence of a ring chromosome 17.
An anaphase lag of a chromosome 21 in a Down syndrome embryo leads to a fraction of euploid cells (2n cells), phenomenon described as "aneuploidy rescue". There is considerable variability in the fraction of cells with trisomy 21, both as a whole and tissue-by-tissue. This is the cause of 1–2% of the observed Down syndromes. [4]
A contiguous gene syndrome (CGS), also known as a contiguous gene deletion syndrome, is a clinical phenotype caused by a chromosomal abnormality, such as a deletion or duplication that removes several genes lying in close proximity to one another on the chromosome.
Changes to chromosome 21 include a missing segment of the chromosome in each cell (partial monosomy 21) and a circular structure called ring chromosome 21. A ring chromosome occurs when both ends of a broken chromosome are reunited.