[Instability of the mitochondrial genome]

A number of manifestations of mitochondrial DNA instability have been reviewed. Differences in organization of mitochondrial genomes of different origin have been regarded as well as variability concerning the genetic code. Examples of molecular heterogeneity of mtDNA and among them insertions and optional introns in Saccharomyces cerevisiae are given. Specific mutations in ascomycets and higher plants have been discussed as an aspect of instability since they cause the appearance of mitochondrial plasmids and episomes. One can regard the rate of mtDNA evolution particularly the high frequency of molecular rearrangement as connected with the fact that some of its regions behave as "egoistic" DNA. According to the Doolittle-Crick concept phenotypical selection always supports any useful function of that DNA, emerging by chance. Therefore we admit that some of the optional insertions into mt genes in S. cerevisiae have the adaptive function. It is also possible that in the course of evolution some higher plants "have learned" to use the DNA's ability to generate plasmids and episomes in order to create new means of gene activity regulation.