In this thesis, the role of mobile genetic elements, transposons (TEs), in genome evolution, genetic diversity creation, adaptation and species invasiveness is described. Transposons are classified as DNA transposons and retrotransposons, which differ in the way they move in the genome. DNA transposons move by the so-called. "cut and paste" mechanism and retrotransposons employ "copy and paste" strategy and are more similar to viruses. Transposons are potent insertional mutagens and can have both positive and negative effects on the host. They are present in the genomes of many organisms, and most of the times constitue a large proportion of the genome. Vertebrates are a group of organisms that are evolutionarily very successful and have structurally and functionally complex genomes that contain all types of TE elements. They are thought to have played a significant role in their evolution. Transposons are controlled at the epigenetic level, via RNA interference or DNA methylation. Activation of TE elements may be due to relaxation of epigenetic control caused by changes in the environment, especially under stress conditions. The adaptability of invasive species, despite their reduced genetic diversity due to the bottleneck effect, is also related to the activity of transposons that can create new variations and diversity. Examples of different species are given.