Transposable elements (TEs) are universal, present in every organism that has been screened for. Since their discovery, they have been thought of both parasitic and useful to the host. Transposition is opposed by several evolutive forces such as deletion, selection and regulation. The evolution of TE copy number once horizontal transfer has occurred, i.e. when one copy of the TE is present in the genome of an individual, is suggested to be influenced by genetic drift. Capy et al. (2005) propose that in order for the TE invasion to be successful in its new genomic environment, the element should contain a high initial transposition rate, since at such a rate the influence of population size decreases. If the transposition rate and population size is low, then random genetic drift becomes important and causes a higher loss frequency of the element. TEs found in the genome of present species are those that had an effective invasion strategy, whereas others are lost through genetic drift. After successful invasion, TE will evolve without any selection pressure, but other intragenomic regulations come into play. Regulation of TE amplification is beneficial to both TE and host, since aggressive TEs will destroy the host and become lost with it; and too repressive hosts will lose a source of genetic variability.
Written by: student 41137673
References:
http://www.nature.com/hdy/journal/v85/n2/abs/6887510a.html
