Fig. 5.

ERV integration time estimation. A The ERV integration time can be estimated based on the divergence of 5′- and 3′-LTRs of an ERV. B The age of an ERV can be estimated based on its orthologous insertions within closely related species. C ERV insertions might undergo segmental duplication. The divergence time of segmental duplicates provides a minimum estimate of the invasion time. D The integration time of an ERV can be estimated based on the occurrence of stop codons within it. The orange vertical lines indicate disruptive mutations, the asterisks (∗) represent stop codons and the green rectangles represent host genes.