Structural traits summary. Simplified view of the different genotypic traits suggested for retroviral phylogeny inference. The branch for Gypsy and Copia represent an imagined midpoint reference in the tree. The number of NC zinc fingers, presence of dUTPase (dUTPasePolB is not indicated), known accessory genes, C-terminal Pro (G-patch) and Pol (GPY/F) motifs are shown. Nucleotide bias was defined to 25 ± 5 %. (↑) shifted upwards; (↓) shifted downwards; (≈) uncertain bias. Exploration of the LTR lengths of the different groups as detected by RetroTector© are shown as boxplots. In addition, the translational strategy may be used in the phylogeny to separate the gammaretroviruses (including class I ERVs) from spuma-like elements (class III ERVs), deltaretroviruses, lentiviruses, alpharetroviruses and the betaretroviruses (class II ERVs) with respective intermediate groups. The Gypsy and Copia are not included in the translational strategy analysis.