Polyploidy

Abstract

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. Polyploidy of individual cells or cell types (endopolyploidy), arising from chromosome replication without cell division, is involved in the normal (e.g., secretory cells) or abnormal (e.g., many cancers) development of organisms. 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. Many plant species, in particular, have both ancient whole-genome duplications and more recent polyploidy events in their ancestry. 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. Polyploids can be generated experimentally by treatment with chemicals such as colchicine or by fusion of diploid nuclei. 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.