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A tetrasomy is a form of aneuploidy with the presence of four copies, instead of the normal two, of a particular chromosome.

Classification and external resources
Specialty medical genetics
ICD-10 Q97 - Q98
MeSH D000782
Orphanet 3305




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.

Autosomal tetrasomiesEdit

Sex-chromosome tetrasomiesEdit