How mutagenic are transposable elements?

Even though transposable elements (TEs) are known to be ubiquitous, studies on mutation rates often overlook this dynamic component of the genome. Fortunately, both our understanding of the mechanisms and assays of movement within and between lineages have expanded. In this review, we aggregate direct estimates of TE mutation rates from the literature to quantify the mutagenicity of mobile DNA. Overall, based on a subset of comparable studies, the mean rate of gain is 1.6 × 10^-3 elements per copy per generation, an order of magnitude faster than the mean rate of loss (1.9 × 10^-4). We discuss challenges for comparing rates across studies and outline the major genotypic and phenotypic consequences of TE movement. In conclusion, TEs can no longer be sidelined as 'junk' given the genetic variation they generate. Instead, we argue the role of TEs as an endogenous mutagen means they demand a more central place in mutation research.