Figure 2

Observed ratios. Observed ratios of full-length proviruses and solo-LTRs on the allosome (X or Z) to the autosome for the genomes of 15 mammals and 3 birds. Vertical lines mark the key ratios $\frac{2}{3}$, 1, $\frac{3}{2}$ and 2. Asterisks mark the genomes we consider as trustworthy and discuss in the Results section. Mammalian full-length provirus ratios typically lie beyond 3/2, the maximum predicted value under an assumption of male-bias. Mammalian solo-LTRs are generally more evenly distributed between autosome and allosome. Mammalian solo-LTRs are also generally relatively less abundant on the allosome than full-length proviruses.