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Figure 1 | Genome Biology

Figure 1

From: Widespread evidence for horizontal transfer of transposable elements across Drosophilagenomes

Figure 1

Natural history of TEs and their hosts. On the left, if TEs are vertically transmitted (VT), their evolutionary history (red) follows that of their hosts (grey). At copy number equilibrium (3), TE abundance is constant along the generations, and speciation events of the hosts cause diversification of TE lineages. The possibility of stochastic loss (5) means that any TE family can be randomly lost over the generations in a given host. In the long term, this would cause the vertical extinction of all TEs from the genomes. On the right, HT of TEs (blue arrow) allows the possibility of recurrent invasions and long term persistence of TEs. TE arrival into a new host by horizontal transfer (HT) (1) is followed by a period of copy number increase (2) until transposition-selection equilibrium is reached (3). Upon speciation and the concomitant diversification of hosts and TEs (4), the stochastic loss of a family in a given lineage (5) can be reversed by HT. However, this should leave a genetic footprint. Neutral genetic differentiation is a direct function of time since divergence. If TEs and host nuclear genes are subject to similar evolutionary forces, the synonymous divergence of vertically transmitted extant orthologous TE families (KSTEs) is expected to be similar to that of the nuclear genes of the hosts (KSNGs) as the same time has elapsed since their split (t0-t2; continuous line). But TEs that jumped between these species have had time to accumulate differences only since the HT event (t0-t1; dotted line), so that reduced levels of divergence relative to host genes are expected.

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