Also found in: Dictionary, Thesaurus, Medical, Wikipedia.


Number of complete chromosome sets in a nucleus: haploid (N), diploid (2N), triploid (3N), tetraploid (4N), and so on.



the number that indicates how many times the set of chromosomes characteristic of the germ cells of a given species is replicated in the cell nucleus. The majority of organisms that reproduce sexually are diploid, that is, each of their somatic cells contains two sets of chromosomes (one for each of the haploid germ cells or gametes). In nature and under artificial conditions, ploidy may change in multiples higher that two (eupioidy); there may also be a loss or gain of individual chromosomes (aneu-ploidy).

Euploid increase of the number of chromosome sets (poly-ploidization) occurs if the chromosomes do not separate during cell division. It may also result from the merging of nuclei containing more than one set of chromosomes. There are two types of polyploidy: autopolyploidy, in which the number of homologous sets of chromosomes is increased, and allopolyploidy, which arises when there is a joining, as a result of hybridization, of the genomes of various species. Nonseparation of genomes can occur only in part of the cells of some tissues (somatic polyploidy, which is characteristic of many multicellular animals and plants). Polyploidization can lead to the formation of new plant species and thus serves as an important factor in their evolution (as well as of unicellular organisms). Its significance for species formation in multicellular animals is apparently limited to par-thenogenetic forms. Aneuploidy leads to serious disruptions of development, which often lead to death of the organism and, therefore, does not play a significant role in evolution. Aneuploid cells are common in malignant tumors.

Methods have been elaborated for artificially altering ploidy. They are used to obtain economically valuable forms of plants and for research purposes (for example, to study the action of genes).

References in periodicals archive ?
Those scallops that reached adult age (1-y age, 6 cm shell height) were evaluated for their ploidy condition through flow cytometry analyses: 0.
Monthly SL and BW were different among the ploidy/site groups and probability values (Table 3) indicate that environment influenced growth rate to a greater extent than oyster ploidy or their interaction.
For almost all plants, regardless of population or ploidy, flowering began the first week of June and continued for 6 wk through midjuly (Fig.
likely due to ploidy reduction and inbreeding depression.
Sebaceous carcinoma of the parotid gland in children: an immunohistochemical and ploidy study.
2009) established that 31% of fern speciation events are accompanied by ploidy increase, as compared to only the 15% in angiosperms (Fig.
It has been reported that cytokines such as interleukin-3 and interleukin-6 (IL-6) influence megakaryocyte ploidy and can lead to the production of more reactive and larger platelets (4).
Thus, it is important to develop a method to verify the ploidy level of organisms after induction or to detect polyploidy in the environment where oyster farming has occurred for long periods of time.
Myriad factors remain unexplored in this species, including the ploidy of sexually and asexually produced eggs, the effects of parasites or other considerations of co-evolution (e.