Abstract
The model of periodic changes in the basic chromosome number x in the long structured phylogenetic branches (LSPB) of some monocotyledons has been developed as a first approximation. A two-stage saltational cryptaffinic transition between two evolutionary static groups has been proposed. In the case of the ancestral group of taxa, the dominating basic chromosome number x is equal to seven or eight; according to our previous study, ITS1 and ITS2 regions of rRNA in these taxa are depleted in cytosine and guanine (Chupov et al., 2007). At the first stage of the cryptaffinic transition, the basic chromosome number significantly increases up to x = 18–30, and rRNA is saturated with cytosine and guanine residues and CpG sequences. At the same time, no significant morphological or taxonomical transformations occur. At the second stage, the x value often becomes equal to 11–12, and critical morphological and taxonomical changes take place. Then, the process of the dC-to-dT transformation becomes predominant in rRNA (Chupov and Machs, 2010). This zone of LSPB can be characterized as the region of the innovation genome reintegration. Then, the basic chromosome number can drop again to x = 7, 8, or even lower, and the process of cytosine burnout continues in rRNA. This process can be periodically repeated in the LSPB.
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