![]() ![]() Many plant species are polyploid, and they can include multiple chromosome sets from one (autopolyploids) or more than one (allopolyploids) ancestral species. Polyploids still have 2n chromosomes, but more than two genomes, so a triploid with three genomes would be 3x a tetraploid, 4x a pentaploid, 5x a hexaploid, 6x an octaploid, 8x or a dodecaploid, 12x. The diploid chromosome number, 2n, refers to the number of chromosomes in a cell of the individual normally producing the germ cells (the sporophyte): a non-polyploid, diploid organism as represented by most higher plants and animals would be described as 2n=2x with the number of chromosomes given. In presenting chromosome numbers or karyotype constitutions, the letter x is used to refer to the basic chromosome number of the ancestor of a polyploid. Polyploidy may occur by the number of chromosomes in a cell doubling because of a failure of chromosome sets to divide at mitosis, by fusion of nuclei from diploid cells, or by a failure of meiosis giving a 2n gamete, so the resulting embryo has at least one extra chromosome set. Tetraploid A species or individual organism having four sets of chromosomes (four genomes or typically 4 times the basic haploid chromosome number of x) in each cell. Polyploid A species, individual organism, or cell having more than two sets of chromosomes (more than two genomes) in each cell nucleus. Many polyploids, particularly among plants, develop normally, and depending on the nature of the polyploidy may be sterile, or undergo meiosis that is indistinguishable from a normal diploid giving viable gametes.Īmphidiploid Autopolyploid Eukaryotes TetraploidĪmphipolyploid A species or hybrid having more than two sets of chromosomes that originate from more than one parental or ancestral species.Īutopolyploid A species or hybrid having more than two sets of chromosomes originating from the same parental or ancestral species. ![]() Polyploids can be generated experimentally by treatment with chemicals such as colchicine or by fusion of diploid nuclei. Polyploid individuals are found occasionally in all groups of eukaryotic organisms as a result of incorrect meiosis, fertilization, or cell division, although most spontaneously occurring animal polyploids are inviable. Many plant species, in particular, have both ancient whole-genome duplications and more recent polyploidy events in their ancestry. Polyploidy or “whole-genome duplication” is an important feature of genome evolution and speciation, and most lineages of plants and animals include rounds of such duplications in their evolutionary history. ![]() Polyploidy of individual cells or cell types (endopolyploidy), arising from chromosome replication without cell division, is involved in the normal (eg, secretory cells) or abnormal (eg, many cancers) development of organisms. Polyploid organisms are eukaryotes that have more than two complete sets of chromosomes (one from each parent or ancestor) in somatic and germline cells of animals, fungi, and plants. In: Reference Module in Life Sciences, Elsevier, ISBN: 978-0-12- 809633-8, (££$$€€) (see for information about the series.) ![]()
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