Genetic and epigenetic aspects of polyploid evolution in plants.

Polyploidy, the condition of possessing more than 2 complete chromosome sets in the same nucleus, is frequent in nature and has implications for a species' prospects for evolution. Newly formed polyploids, so-called neopolyploids, undergo a wide spectrum of genomic changes upon genome merger and duplication. Here, we review recent literature describing genomic and transcriptomic changes along the pathway from neoallopolyploid formation to the stabilization of species and diversification at the allopolyploid level. We begin by reviewing pathways of polyploid formation and discuss the effects of genome doubling and hybridization on chromosome pairing. We then review our knowledge of epigenetic changes in allopolyploids, followed by a consideration of the effects of these structural genomic and epigenetic changes on the transcriptional activity of genes in allopolyploids. We discuss the effects of changes in gene expression in polyploids with respect to current evolutionary theory. Finally, we draw attention to the general question of the relationships between genomic and transcriptomic alteration and incipient diversification among sibling polyploid lines and populations.