Fig. 1. Comparison of (a) traditional view of polyploid formation with (b) new or revised view. The traditional view envisioned each polyploid species forming only once, resulting in a new species that was genetically uniform (or nearly so). The new view suggests that each polyploid species forms over and over again from different parental genotypes generating a diverse array of polyploid genotypes. Subsequent hybridization among these polyploid genotypes and recombination result in additional genetic variability.

Fig .2. Comparison of (a) traditional view of genomic evolution subsequent to polyploid formation with (b) new or revised view. The classic view of genome evolution suggested that interactions between the parental genomes of an allopolyploid were minimal. Recently, it has become apparent that both intra- as well as inter-genomic rearrangements occur. (b) In this example, arrows indicate genomic rearrangements – intragenomic rearrangements are represented by hatched areas on chromosomes from ‘diploid B’; intergenomic rearrangements are represented by translocation of ‘black’ or ‘white’ chromosomal segments between the genomes of ‘diploid A’ and ‘diploid B’. The degree of genomic change can also be influenced by cytoplasmic–nuclear interactions. In a newly formed allopolyploid, there are adverse interactions between the nuclear genome contributed by the male parental diploid and both the nuclear and cytoplasmic genomes of the female parental diploid; genome adjustments must occur to restore nuclear–cytoplasmic compatibility. Available data suggest that the nuclear genome of maternal origin experiences less change than does the paternal nuclear genome. Other evidence implicates transposable elements in the genome reorganization that has been detected in polyploids.