Interspecies hybridization and polyploidy play a major role in the processes of speciation and progressive evolution in plants. There are three possible ways of transforming hybrid genomes, which is somehow related to speciation in plants: 1). Introgression – the hybrid genome is stabilized by backcrossing with parental species without polyploidization – this is how such species as the Finnish spruce arose. 2). Genome polyploidization – the hybrid genome becomes stable while retaining doubled sets of chromosomes of the parent species. It can be called a “good” (eu-) polyploid. Most genomes/karyotypes of numerous polyploid polyploid plant species are in the eupolypoloid state. This is a fast and effective way of speciation, but speciation at an already mastered level of evolutionary complexity. 3). Dysploidy and secondary diploidization of the genome – intensive genomic rearrangements occur in the hybrid and polyploid genome and karyotype. A significant part of the duplicated copies is pseudogenized or deleted. The number of chromosomes in the haploid genome is radically reduced, often to a level close to the primary diploid chromosome numbers “2x”. Different individuals of a species that have embarked on the path of stochastic “fractionation” of the genome and dysploidy, retain different sets of unique and multiplied during WGD protein-coding genes, transposons, short interfering and long non-coding RNAs. In this case, intraspecific genomic and epigenetic polymorphism increases radically, that provides rich material for natural selection. Diploidization of genomes and karyotypes makes combinations of gene alleles and neogens, previously buffered in the polyploid state, available for testing by natural selection. Massive gene losses during genome fractionation can have a most unexpected effect on the phenotype, which often takes neotenous forms. Some neotenic morphotypes with diploidized and fractionated postpolyploid genomes, “hopeful monsters”, have such an original combination of gene families and morphological features that gives their carriers a chance to become the founder of a new large taxon, tribe, family, class.
A. V. Rodionov (Wed,) studied this question.