polysomy /pol″isō′mē/ , the presence of more than two copies of a chromosome in an otherwise diploid somatic cell as the result of chromosomal nondisjunction during meiosis. The chromosome may be duplicated three (trisomy), four (tetrasomy), or more times. Males with Klinefelter’s syndrome may have a genotype of XXY, XXXY, or XXXXY. Polysomic females with three, four, or five X chromosomes may have a higher frequency of intellectual disability.
