The unity of the whole and freedom of parts: Facultativeness principle in the hereditary system
Mikhail D. Golubovsky · Russian Journal of Genetics Applied Research · 2011
Facultativeness in the genome structure and function reflects the general principle of life organization and evolution: the unity of the whole and the freedom of parts . The genome, or cell hereditary system code, maintains and transfers hereditary information both structurally and dynamically. The generalized genome concept presents a genome as an ensemble of both obligate and facultative elements. Template processes (Replication, Transcription and Translation) and Basic genetic processes (Repair, Recombination and Segregation) are capable of functional facultativeness and dynamic (epigenetic) modifications. It is reasonable to discriminate among three kinds of heritable changes: mutations, variations and epigenetic modifications. Structural genome facultativeness is expressed as a subdivision of cell DNA and RNA elements into two subsystems: Obligate genetic elements (OGEs) and Facultative genetic elements (FGEs). FGEs include various kinds of repeated sequences, mobile elements, amplicons, inserted viral and foreign DNA, B-chromosomes, plasmids and cytobionts. The abundance and intracellular topography of FGEs are different in different cells, tissues and individuals. Changes in the structure or order of OGEs correspond to classical mutations. For diverse changes in the number or cell/tissue topography of FGEs the term variations seems appropriate. Mutations and variations significantly differ in the pattern of their occurrence. Variations may occur simultaneously in many cells/individuals and are induced by nonmutagenic factors. Spontaneous hereditary changes in nature usually occur in the system ENVIRONMENT—FGEs—OGEs via a two-step pathway. FGEs are first to respond to both internal and external environmental challenges. Then their activation induces gene/chromosomal mutations. Both variations and epigenetic changes (epivariations and epimutations) may have non-Mendelian features, sometimes reminding the phenomenon of inheritance of acquired characteristics.