On the features of evolutionary process in plants: diploidization of the genomes and karyotypes

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As estimated by karyosystematists, from 30 to 50 % of land plant species exhibit polyploid karyotypes, respectively, from 50 to 70 % of plants are diploids. One of the mechanisms of diploidization of a neopolyploid karyotype is chromosomal rearrangements leading to a change in the chromosome number in genomes - so-called dysploidy. In parallel with the processes of karyotype diploidization, contributing to it and supplementing it, there are processes of structural and epigenetic diploidization of the genome, the loss of part of the duplicated genes. It may be that the role of genome polyploidy in plant evolution lies primarily in the fact that this ephemeral state is primarily an effective way to destabilize the genome, a source of many new combinations of alleles that pass through a rigid selection sieve and are realized later at the secondary diploid stage. The transition from a polyploid to a diploid state is justified by the fact that neopolyploids cannot provide a high percentage of gametes carring balanced chromosome sets due to problems with chromosome pairing in meiosis I. The mechanisms of transition to strict pairwise chromosome pairing are such that automatically leads to diploidization of both the genome and the karyotype. It is also important that the diploid karyotype provides more stringent, faster, more efficient selection of adaptively important new combinations of alleles, thereby contributing to the accumulation of taxonomically significant traits, speciation, and, as a result, to progressive evolution.