A tetrasomy is a form of

aneuploidy Aneuploidy is the presence of an abnormal number of chromosomes in a cell (biology), cell, for example a human somatic (biology), somatic cell having 45 or 47 chromosomes instead of the usual 46. It does not include a difference of one or more plo ...

with the presence of four copies, instead of the normal two, of a particular

chromosome A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most import ...

Causes

Full

Full tetrasomy of an individual occurs due to non-disjunction when the cells are dividing (

meiosis Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...

I or II) to form egg and sperm cells ( gametogenesis). This can result in extra

s in a sperm or egg cell. After fertilization, the resulting fetus has 48

chromosomes A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most importa ...

instead of the typical 46.

Autosomal tetrasomies

* Cat eye syndrome where partial tetrasomy of chromosome 22 is present * Pallister-Killian syndrome (tetrasomy 12p) * Tetrasomy 9p * Tetrasomy 18p *

Tetrasomy 21 A tetrasomy is a form of aneuploidy with the presence of four copies, instead of the normal two, of a particular chromosome. Causes Full Full tetrasomy of an individual occurs due to non-disjunction when the cell division, cells are dividing (mei ...

, a rare form of Down syndrome

Sex-chromosome tetrasomies

* Tetrasomy X * XXYY syndrome * XXXY syndrome

External links

{{Chromosomal abnormalities Cytogenetics Chromosomal abnormalities