Polyploidy is a condition in which the cells of an organism have more than one pair of chromosomes. Most species whose cells have nuclei are diploid, meaning they have two complete sets of chromosomes. Polyploidy may occur due to abnormal cell division, either during mitosis or from the failure of chromosomes to separate during meiosis or from the fertilization of an egg by more than one sperm. It can also be induced in plants and cell cultures by some chemicals, such as colchicine and oryzalin, which can result in chromosome doubling.
Polyploidy is common among plants, as well as among certain groups of fish and frogs. There are several advantages to being polyploid, such as hybrid vigor or heterosis, whereby the polyploid offspring of two diploid progenitors is more vigorous and healthy than either of the two diploid parents. However, there are also potential disadvantages of polyploidy, such as changes in gene expression. Polyploidy has been viewed as a major driver in evolution, and its influence on genome and chromosome evolution has been at the center of many investigations.
