Transposable elements and the evolution of genome size in eukaryotes

Compared to prokaryotes, genomic sizes in eukaryotes vary more than 200000 fold. In fact, the wide variation in genome size observed among eukaryotic species is more closely correlated with the amount of repetitive DNA than the number of coding genes.

Major types of repetitive DNA include transposable elements, satellite DNAs, and simple sequences. Transposable elements are the DNA of a single cell that undergo recombination. Transposable elements never exist independently but are always part of chromosomal or plasmid DNA. The movements of these elements are called transposition. Transposable elements are responsible for a significant proportion of the observed variation among many groups.

The ways in which transposable elements contribute both directly and indirectly to genome size variation are explored. Actually, there aren’t enough evidence to support the existence of a linear relationship between total transposable element DNA and genome size. The partial release of transposable element copy number appears to be a major characteristic of large genomes. Animals and plants have different genomic patterns for insertion of repeats. Specifically, in animals, most repeats integrate into intron DNA, but in plants, most repeats integrate into intergenic DNA.

In conclusion, if genome size is adaptive under certain conditions, transposable elements may appear to be an important mechanism for providing some of the variation in this trait, more specifically, where natural selection acts.

Reference :
Margaret G. Kidwell. Department of Ecology and Evolutionary Biology, The University of Arizona, Tucson, Genetica. 2002. 115: 49–63.

By:
Jie Hui Ng
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