MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedonyuk 2010

BIOLOGY

SECTION 1. BIOLOGICAL FOUNDATIONS OF HUMAN VITAL ACTIVITY

1.3. MOLECULAR-GENETIC AND CELLULAR LEVELS OF LIFE ORGANIZATION

1.3.3. Hereditary apparatus of eukaryotic cells and its functioning - molecular level

Mobile Genetic Elements

Mobile (migrating) genetic elements (MGEs) are DNA nucleotide sequences capable of moving (transposition) within a given genome or between genomes. They have been found in the genomes of Viruses, Bacteria, Yeasts, Drosophila, mice, and others. They are associated with the occurrence of Mutations and variations. Thanks to MGEs, organisms can acquire ready-made genes from other organisms, which is of great importance for evolution. MGEs were first discovered by the American geneticist B. McClintock (1947) in maize and named "controlling elements" (Nobel Prize, 1983). They have no intrinsic phenotypic expression of their own and manifest themselves through alterations in the genes within whose loci they reside or which they influence from a distance. For instance, they determine changes in corn kernel coloration. It is believed that there are at least two mechanisms of MGE mobility. The first involves the excision of the mobile element from one site on a chromosome and its insertion into another. In the second mechanism, the mobile element retains its original position while generating a copy of itself, which is subsequently inserted elsewhere.

MGEs also include bacterial IS elements and Transposons. IS elements (insertion sequences) average about 1000 bp in length and carry no genes other than those required for transposition. They are incapable of autonomous Replication and feature inverted repeats at their ends, which induce all types of chromosomal rearrangements. The genes of IS elements encode the transposase enzyme. Utilizing transposase and inverted repeats, IS elements integrate into the bacterial chromosome. Transposons (Tn elements) are more complex mobile genetic elements formed from IS elements. In addition to genes responsible for transposition, they may carry other genes, such as those conferring Antibiotic Resistance.