Abstract: Polyploidy is widely acknowledged as a major mechanism of adaptation and speciation in plants. Recent estimates suggest that 70% of all angiosperms have experienced one or more episodes of polyploidization. Interdisciplinary approaches combining phylogenetic and molecular genetic perspectives have enhanced our awareness of the myriad genetic interactions made possible by polyploidy. In this paper, cytological mechanisms of polyploid formation and processes and mechanisms of gene and genome evolution in polyploids are reviewed. In many cases, spontaneous polyploids have cytotypes that appear to have been formed by the union of reduced and unreduced gametes. Recent studies demonstrate that most polyploid species have formed recurrently from different populations of their progenitors. Genes duplicated by polyploidy may retain their original or similar function, undergo diversification in protein function or regulation, or one copy may become silenced through mutational or epigenetic means. Duplicated genes also may interact through inter-locus recombination, gene conversion, or concerted evolution. Extensive and rapid genome restructuring can occur after polyploidization. These include inter-genomic chromosomal exchanges, non-Mendelian genomic evolution in nascent polyploids, inter-genomic invasion, and cytonuclear stabilization. Continued application of molecular genetic approaches to questions of polyploid genome evolution holds promise for producing lasting insight into processes by which novel genotypes are generatedand ultimately into how polyploidy facilitates evolution and adaptation.

Key words: Polyploid plants, Multiple origins, Genome evolution