Figure 2.

Quantities of constrained sequence (g_sel) estimated across a range of diverse metazoan species' pairs. Estimates of constrained sequence in eutherian mammalian (red), avian (dark blue), teleost fish (brown), and fruit fly (light blue) species' pairs. For mammalian estimates, a dramatic drop-off in estimates of conservation is associated with increasing divergence between species' pairs, which is not seen in simulations (Fig. 3). The indicative sweep (shaded) suggests that the true quantity of functional material in mammalian genomes may be around 300 Mb (10% of the human genome). The range for human and macaque represents several estimates with varying parameters for the calibration of the neutral model. Consequently, these values may underestimate the true level of constraint. Our highest estimate of conserved sequence in mammals is between mouse and rat, for which we estimate 189.0–258.4 Mb of functional sequence.