The role of Transposable Elements in the Human Genome and their contribution to Evolution
Ravesteyn, T.W. van
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Transposable elements (TEs) were originally discovered in Zea mays in the 1950s by Barbara McClintock (MCCLINTOCK 1956). In essence, they are genetic elements that are mobile and can move from one position to another within genomes. This concept fundamentally changed the view on genomes. Instead of rather static entities, it suggested that genomes are actually highly dynamic (Georgiev 1984). The draft of the human genome revealed that nearly half of the human genome is derived from transposable elements (Jurka et al. 2005; Lander et al. 2001). Britten and Davidson hypothesized that repetitive elements can act to distribute regulatory sequences throughout the genome, and thereby enriching, possibly even creating, whole pathways (Britten and Davidson 1971). The adoption of a TE to a new function by the genome is called “exaptation” (Gould and Vrba 1982), and would enhance genetic innovation. In this sense, they can be viewed as catalysts of evolution because their contribution to variation might have increased the speed of evolution on the human lineage (Britten 2010). Here, I will present an overview of the role of TEs in the human genome and their suggested influences on human evolution. In summary, it is obvious that TEs are really an integrated part of our genomes. It seems that the reduction of effective population size during evolution enabled the accumulation of TEs in most of the eukaryotic organisms. TEs provided the necessary base pairs which were needed to generate new genes and to acquire regulatory functions. They had probably the most profound influences on genome architecture in the early times of evolution and during moments of rapid population expansions. During following evolutionary periods TE derived fragments may have evolved slowly into functional elementsIn addition to effects caused by direct insertion, it seems that TEs had a profound impact on genome evolution by recombination events. The immense TE copy number within the human genome increases the chance of recombination events which can lead to structural variation such as genome duplications, deletions and inversions. Thus, TEs may also affect genome structure after insertion by TE mediated recombination events. It seems difficult to find TEs that can be really related to recent human evolution, the identification of recent integrations might learn us more about the mechanism of transposition, evolutionary selection in the human lineage and the current effect of TE activity on human health.