It has been also suggested that RM systems are maintained in evolution because they participate in generating bacterial diversity by promoting homologous recombination [ 4] or because they act as as "selfish" genetic elements that undergo extensive horizontal transfer [ 5].
Of course, if the fixation of slightly deleterious mutations is followed by that of slightly advantageous mutations, the function of the gene can be maintained in long-term evolution.
Once methylation is set up, only methylation in the CG context, which does not rely on siRNA production, can be maintained in the course of evolution leading to high methylation only in CG sequence contexts [ 43].
The genome may be more tolerant of mutation in the context of tumorigenesis, in which homeostasis need not be maintained in the whole organism, than in the evolution of species, in which this homeostatic constraint must be obeyed.
Orthology can be confirmed by obtaining mapping data of surrounding genes, with the assumption that groups of syntenic genes would remain in close proximity through evolution, and therefore be maintained in similar segments of DNA.
Due to selection constraints in crown morphological evolution, an effective occlusion has to be maintained in order to ensure functional continuity [9].
In fact, cladistic analyses, indicating that the appendix has evolved independently at least twice (once in diprotodont marsupials and once in Euarchontoglires), show a highly significant (P < 0.0001) phylogenetic signal in its distribution, and has been maintained in mammalian evolution for 80 millions years or longer [ 15].
We conclude, that transcriptional autoregulatory feedback loops constitute a core transcriptional network motif and their conservation has been maintained in higher vertebrate organism evolution.
This suggests that LGT-transferred segments are maintained in situ during subsequent clonal evolution.
