Aneuploidy is an abnormal number of chromosomes in the cells of an individual. The main aneuploidies of the human species and their respective conditions are: the nullisomies (absence of any chromosome pair of the species, often incompatible with life); the monosomies (absence of a chromosome from a pair, for example, Turner’s syndrome, 44 + X); the trisomies (an extra chromosome, for example, the triple X syndrome, 44 + XXX, or the Edwards syndrome, trisomy 18, 45 + XY or 45 + XX).