noun, plural: tetrasomies
(genetics) A type of aneuploidy characterized by the gain of two extra chromosomes of one type, and is designated as 2N+2
Aneuploidy is a chromosomal variation due to a loss or a gain of one or more chromosomes resulting in the deviation from the normal or the usual number of chromosomes. The different conditions of aneuploidy are nullisomy (2N-2), monosomy (2N-1), and polysomy (e.g. trisomy and tetrasomy). Polysomy is a condition where there is more than one copy of the chromosome relative to the normal. Trisomy (2N+1) and tetrasomy (2N+2) are examples of polysomy.
Trisomy is a polysomy characterized by an extra copy of a particular chromosome. Thus, the chromosomal composition is represented by 2N+1. A cell or an organism exhibiting monosomy is referred to as trisomic. Tetrasomy is a type of aneuploidy where there is a gain of extra two chromosomes of the same type. The chromosomal composition is represented by 2N+2. A cell or an organism exhibiting monosomy is referred to as tetrasomic.
Nondisjunction during meiotic division may cause polysomies. When the chromosome(s) fail to separate during meiosis, the resulting gametes would have an atypical chromosomal number. When such gamete became involved in fertilization, the fetus would be polysomic. For instance, an extra chromosome 21 would lead to trisomy 21 syndrome (or Down syndrome). Klinefelter’s syndrome (XXXY syndrome) is an example of tetrasomy where there is an extra pair of sex chromosomes.