Distribution of three categories of HERV-W elements in genic/intergenic regions and distribution of intronic HERV-W elements on sense and anti-sense strands, respectively. 1Total number of intronic HERV-W elements, 2 indicates number of proviruses and solo LTRs. * indicate expected number based on random integration (i.e. 50% on each strand). Pro, solo and pse indicate proviruses, solo LTRs and pseudoelements, respectively. aChi-square test, bFisher's exact test. P-values <0.05 were considered significant.