A sense of self: the role of DNA sequence elimination in allopolyploidization.

Polyploid organisms contain a number of chromosomes that is some multiple of x (basic chromosome number) greater than the 2 x content of related diploid species. Winkler (1916) introduced the term in a study of vegetative grafts in Solanum, when he discovered tetraploid plants regenerated from callus tissue on cut stems of diploid S. nigrum . Winge (1917) observed that interspecific hybrids give rise to hybrid plants that are sterile as a result of the failure of correct chromosome pairing at meiosis; he proposed that spontaneous chromosome doubling, resulting from accidental somatic doubling in mitosis or nonreduction in meiosis, could convert such hybrids into a fertile type. As illustrated by these two early reports, polyploidy can arise from a doubling of a single genome (autopolyploidy) or from the merger of two distinct genomes after hybridization (allopolyploidy). Since then, polyploidy has been found to be very common in plants. Polyploidization is currently viewed as a highly dynamic process and a major force in the evolution of higher plants (Soltis and Soltis, 1995). Wendel (2000) stated that certainly 50% and perhaps more than 70% of angiosperms have experienced chromosome doubling at some point in their evolutionary histories, and Grant (1981) reported an estimated frequency of as high as 95% among pteridophytes. Genomic analysis of a growing number of organisms may produce further upward revisions of these numbers as numerous previously recognized diploids, including Arabidopsis (Grant et al., 2000), maize (Gaut and Doebley, 1997), soybean (Shoemaker et al., 1996), cotton (Muravenko et al., 1998), and sorghum (Gómez et al., 1998), are discovered A Sense of Self: The Role of DNA Sequence Elimination in Allopolyploidization