Fig. 4

Evolution of ERVs in the pig genome. a ERVs were classified into 18 ERV families (ERV1–18) based on the phylogenetic tree inferred by using the Neighbor-joining method with the MEGA7 program, and the reference RT sequences from species other than pigs are included for comparison, shown with dots and described in the methods. b Structural schematics of the ERV6A and ERV6B, which featured LTR-gag-pol-env-LTR and were presumed to be active. Gag_MA: Matrix protein (MA), p15; Gag_p30: Gag P30 core shell protein; RVT_1: Reverse transcriptase (RNA-dependent DNA polymerase); RNase H-like: RNase H-like domain found in reverse transcriptase; rve: Integrase core domain; MLV-IN_C: Murine leukemia virus (MLV) integrase (IN) C-terminal domain; TLV_coat: ENV polyprotein (coat polyprotein) (c) Age distribution of pig ERV classes. d Age distribution of the youngest pig ERV subfamilies (ERV6A and ERV6B). e Insertion polymorphism detection of the youngest pig ERV subfamilies (ERV6B) by PCR. Breed name abbreviations are the same as those in Fig. 1f. The x-axis represents the insertion age (Mya), and the y-axis represents the percentage of the genome composed of retrotransposon families/subfamilies (%) in Fig. c, d