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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.
Monosomy. Schematic karyogram of a human, showing the normal diploid karyotype. It shows annotated bands and sub-bands as used for the nomenclature of chromosome abnormalities including partial monosomies. It shows 22 homologous chromosomes, both the female (XX) and male (XY) versions of the sex chromosome (bottom right), as well as the ...
[5] [6] Aneuploidy can be full, involving a whole chromosome missing or added, or partial, where only part of a chromosome is missing or added. [5] Aneuploidy can occur with sex chromosomes or autosomes. [citation needed] Rather than having monosomy, or only one copy, the majority of aneuploid people have trisomy, or three copies of one chromosome.
Henry Turner. Turner syndrome (TS), also known as 45,X, or 45,X0, is a genetic disorder in which a females cells have only one X chromosome or are partially missing an X chromosome (sex chromosome monosomy) leading to the complete or partial deletion of the pseudoautosomal regions (PAR1, PAR2) in the affected X chromosome. [ 2 ][ 6 ][ 7 ] Most ...
Chromosome 21 is one of the 23 pairs of chromosomes in humans. 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 ...
Euploidy and aneuploidy describe having a number of chromosomes that is an exact multiple of the number of chromosomes in a normal gamete; and having any other number, respectively. For example, a person with Turner syndrome may be missing one sex chromosome (X or Y), resulting in a (45,X) karyotype instead of the usual (46,XX) or (46,XY).
Full tetrasomy of an individual occurs due to non-disjunction when the cells are dividing (meiosis I or II) to form egg and sperm cells (gametogenesis). This can result in extra chromosomes in a sperm or egg cell. After fertilization, the resulting fetus has 48 chromosomes instead of the typical 46.
Partial aneuploidy can also occur as a result of unbalanced translocations during meiosis. [11] Deletions of part of a chromosome cause partial monosomies, while duplications can cause partial trisomies. If the duplication or deletion is large enough, it can be discovered by analyzing a karyogram of the individual.