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Number of complete chromosome sets in a nucleus: haploid (N), diploid (2N), triploid (3N), tetraploid (4N), and so on.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



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).

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
dihaploid clones exhibiting better resistance than their parents.
than their dihaploid offspring (Peloquin & Hougas, 1960; De Maine,
and anther-derived dihaploid potato Solanum tuberosum L.).
RAPD markers for confirmation of somatic hybrids in the dihaploid breeding of potato (Solarium tuberosum L.).
Detection of a quantitative trait locus for both foliage and tuber resistance to late blight [Phytophthora infestans (Mont.) de Bary] on chromosome 4 of a dihaploid potato clone (Solanum tuberosum subsp.
This approach was used to generate female-derived parthenogenic haploids in Nicotiana rustica (Ivanov, 1938) and tomato (Ecochard et al., 1974) among others, or to reduce tetraploids to dihaploids in blackberry (Naess et al., 1998).
These factors often limit early generation testing in a conventional breeding program since seed of selected lines would be difficult to obtain after the lodging evaluations are complete, in order to reduce the problems in the lodging evaluation process, the production of homozygous dihaploid lines via anther culture (21, 33) before evaluation would be a reasonable alternative.
Cytological studies on diplandroid production in a dihaploid potato clone and its correlation with seed set in 4x-2x crosses.
Collonnier et al., "Androgenic dihaploids from somatic hybrids between Solanum melongena and S.
Comparison of different pollen viability assays to evaluate pollen fertility of potato dihaploids. Euphytica 56: 143-148.
Current status in production and utilization of dihaploids from somatic hybrids between eggplant (Solanum melongena L.) and its wild relatives.
Using dihaploids and single seed descent during selfing, the latter authors showed that either linkage disequilibrium, pleiotropy, or both factors may cause a genetic correlation, depending on the traits.