Mobile genetic elements have been identified in all studied so far animal species , fungi , and Protozoa . They form a significant component of plant genomes . They are subject to intensive processes of amplification , and then are inserted in new places. Mobile devices are commonly divided into two large classes . The first is the retrotransposons , created with the participation of RNA and reverse transcriptase ; This second class of DNA transposons , in which the process of creating new copies and their movement is mediated by DNA and transposase .

Retroelements constitute a large fraction of the repetitive DNA of eukaryotic genomes. They include LTR (Long Terminal Repeat) and non-LTR retrotransposons, lacking the long terminal repeats and subdivided into LINEs (Long Interpersed Nuclear Elements) and SINEs (Short Interspersed Nuclear Elements), have been discovered as ubiquitous components of nuclear genomes in many species. LINEs are able to transpose autonomously, while non-autonomous SINEs depend on the reverse transcription machinery of other retrotransposons.

Our understanding of the evolution of DNA content in angiosperm plants has improved in recent years. Genomes in angiosperms vary in DNA content over 1000-fold. Variations in plant genome size are primarily due to differences in ancestral polyploidy and the periodic burst in activity of retroele- ments. Genomic data show a strong correlation between the size of genome and the amount of retroele- ments. Gene duplication have contributed to the functional divergence of the duplicates, and have become a strong evolutionary force.

The mechanisms of sex determination in plants.