Polyploid cells and organisms are those containing more than two paired (homologous) sets of chromosomes. Most eukaryotic species are diploid, meaning they have two sets of chromosomes—one set inherited from each parent. However, polyploidy is found in some organisms and is especially common in plants. In addition, polyploidy also occurs in some tissues of animals that are otherwise diploid, such as human muscle tissues. This is known as endopolyploidy. Prokaryotes are haploid organisms, with only a single chromosome in each cell. Most eukaryotes have diploid cells, but produce haploid gametes by meiosis. In plants and multicellular algae the gametophyte generation is haploid, and produces gametes by mitosis. A monoploid has only one set of chromosomes, and the term is usually only applied to cells or organisms that are normally diploid. Male bees and other Hymenoptera, for example, are monoploid.
olysomy is a condition in which an otherwise diploid organism has at least one more chromosome than normal, i.e. the number of a particular chromosome is not diploid - there may be three or more copies of the chromosome rather than the expected two copies. The genotype or phenotype of an aneuploid organism differs by one chromosome or a small number of chromosomes as compared to the natural genotype.Polysomy is a type of aneuploidy in which a set of chromosomes has more chromosomes than normal.The suffix -somy is used to name aneuploid karyotypes. This is not to be confused with the suffix, -ploidy, used for euploid karyotypes. Polysomy is usually caused by non-disjunction (the failure of a pair of homologous chromosomes to separate) during meiosis, but may also be due to a translocation mutation.