polyploidy (redirected from Duodecaploidy)

polyploidy [′päl·i‚plȯid·ē]

(genetics)

The occurrence of related species possessing three, four, or larger multiples of the haploid set of chromosomes.

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Polyploidy

The occurrence of related forms possessing chromosome numbers which are multiples of a basic number (n), the haploid number. Forms having 3n chromosomes are triploids; 4n, tetraploids; 5n, pentaploids, and so on. Autopolyploids are forms derived by the multiplication of chromosomes from a single diploid organism. As a result the homologous chromosomes come from the same source. These are distinguished from allopolyploids, which are forms derived from a hybrid between two diploid organisms. As a result, the homologous chromosomes come from different sources. About one-third of the species of vascular plants have originated at least partly by polyploidy, and as many more appear to have ancestries which involve ancient occurrences of polyploidy. The condition can be induced artificially with the drug colchicine and the production of polyploid individuals has become a valuable tool for plant breeding.

In animals, most examples of polyploidy occur in groups which are parthenogenetic, or in species which reproduce asexually by fission. See Breeding (plant), Chromosome aberration, Gene, Genetics, Plant evolution, Speciation

In addition to polyploid organisms in which all of the body cells contain multiples of the basic chromosome number, most plants and animals contain particular tissues that are polyploid or polytene. Both polyploid and polytene cells contain extra copies of DNA, but they differ in the physical appearance of the chromosomes. In polytene cells the replicated copies of the DNA remain physically associated to produce giant chromosomes that are continuously visible and have a banded pattern. The term polyploid has been applied to several types of cells: multinucleate cells; cells in which the chromosomes cyclically condense but do not undergo nuclear or cellular division (this process is termed endomitosis); and cells in which the chromosomes appear to be continually in interphase, yet the replicated chromosomes are not associated in visible polytene chromosomes. See Chromosome, Chromosome aberration, Genetics, Mitosis