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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]
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]
Aneuploidy is the presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46. [ 1][ 2] It does not include a difference of one or more complete sets of chromosomes. A cell with any number of complete chromosome sets is called a euploid cell.
Robertsonian translocation ( ROB) is a chromosomal abnormality where the entire long arms of two different chromosomes become fused to each other. It is the most common form of chromosomal translocation in humans, affecting 1 out of every 1,000 babies born. [1] It does not usually cause medical problems, though some people may produce gametes ...
Nondisjunction during mitosis leads to one daughter receiving both sister chromatids of the affected chromosome while the other gets none. [ 2][ 3] This is known as a chromatin bridge or an anaphase bridge. Mitotic nondisjunction results in somatic mosaicism, since only daughter cells originating from the cell where the nondisjunction event has ...
Patau syndrome is the result of trisomy 13, meaning each cell in the body has three copies of chromosome 13 instead of the usual two. A small percentage of cases occur when only some of the body's cells have an extra copy; such cases are called mosaic trisomy 13. [citation needed]
Trisomy X occurs via a process called nondisjunction, in which normal cell division is interrupted and produces gametes with too many or too few chromosomes. Nondisjunction is a random occurrence, and most girls and women with trisomy X have no family histories of chromosome aneuploidy .
1 per 5,000 births [ 3] Trisomy 18, also known as Edwards syndrome, is a genetic disorder caused by the presence of a third copy of all or part of chromosome 18. [ 3] Many parts of the body are affected. [ 3] Babies are often born small and have heart defects. [ 3] Other features include a small head, small jaw, clenched fists with overlapping ...