Evolutionary alternation of diploidy and polyploidy

The figure shows the possible paths that result in the sudden transition from diploidy to polyploidy and the gradual transition from polyploidy to diploidy. The hybridization events that result in Allopolyploidy are also illustrated. For simplicity, not all possible paths are drawn. Triploids, for example, are shown contributing to autotetraploids but they can also contribute to allopolyploids. For each ploidy form, the haploid genome is represented by a coloured circle or oval inside the beige-filled nuclear shape. Genomes that are illustrated by ovals reflect the increased gene number that results from the retention and subfunctionalization of duplicates during diploidization. Circles or ovals of different colours represent diverged genomes. Highly unstable ploidy forms have dashed nuclear contours. A and B represent genome types and N is the gametic chromosome number.