ABSTRACT
The evidence for genome reorganizations occurring during the cell cycle comes from cytogenetic experiments showing that several rearrangements can be observed during serial divisions of cells. The observations on the relationship between the capacity of cells to proliferate and the potential for recombinational events of their genome led to a new paradigm for the explanation of the mechanisms determining the long-term growth potential of certain mitotic cell compartments. Telomeres also seem to prevent aberrant recombinations; hence, modifications at the chromosome ends may explain the increased frequency of ring chromosomes and of dicentric chromosomes known to occur during cell aging. Amplification of extrachromsomal circular DNA was also found to increase in human lymphocytes during aging of the organism; the amplification of restricted size classes of circular DNAs occurs only in the latter part of the human life span. A reduction of the methylation level of the c-myc gene, was described in T cells during aging.
