Evolution: a new mechanism of genome size variation linked to the size of organisms discovered in tunicates

Publication from the IGFL in Current Biology on April 1st, 2019. The genome, which corresponds to the whole DNA content of a cell and is characteristic of an organism, can present big variations in size between species. If this size does not correlate with organismal "complexity", it is not clearly established yet if bigger or smaller genomes could be adaptive. Several mechanisms can impact genome size : duplications, deletions, and multiplication of particular sequences called transposable elements. These sequences, which can insert and propagate in genomes, are mostly neutral for the host, or sometimes deleterious if they insert into or next to a gene. They represent at least 45 % of the human genome. Correlations between transposable element coverage and genome size have already been observed in animals or plants, involving large transposable elements described as "autonomous" since they encode the proteins needed for transposition.