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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 ?
than their dihaploid offspring (Peloquin & Hougas, 1960; De Maine,
Mapping of extreme resistance to PVY (Ry sto) on chromosome XII using anther-culture-derived primary dihaploid potato lines.
However, SNPs can readily be used in potatoes by reducing autotetraploid potatoes to dihaploid families (Simko, 2004; Velasquez et al.
Kutsaga 110 is an anther-derived dihaploid from the cross TW 438 x Kutsaga 51E (Anne Jack, personal communication, 2000).
tuberosum (4x) to give rise to a 6x endosperm, which is able to support the development of a dihaploid (2x) embryo from the unfertilized S.
These germplasms may have potential for dihaploid breeding, attaining cytoplasmic diversity, characterizing cytoplasmic organelles and facilitating wide crosses.
The influence of "genetic background" can be illustrated by comparisons between pairing in a polyploid species, pairing in the dihaploid or polyhaploid derived from it, and pairing in different hybrid combinations.
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.
Current status in production and utilization of dihaploids from somatic hybrids between eggplant (Solanum melongena L.