Tetrasomy

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 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.