Polyploidy in angiosperms

Polyploidy has played a major role in higher plant evolution. Most flowering plants are polyploid, and many are distinct in combining the diploid nuclear genomes from two or more different ancestral species or genera (allopolyploids). Recently, molecular techniques have offered powerful new tools for studying the origin and evolution of polyploids. Genomic in situ hybridization allows unequivocal identification of allopolyploids and visualization of their ancestral genomes. Studies of restriction fragment length polymorphism have shown that maize - hitherto generally viewed as a diploid - is really a tetraploid, and that multiple origins are common, if not the rule, for polyploid plant species. It appears that after polyploid formation, considerable and sometimes very rapid changes in genome structure and gene expression have occurred.