As shown in Fig. 1, the linear trend is present, notwithstanding the low power to detect variance components attributable to individual chromosomes. The figure demonstrates a trend that is likely to be stronger with increasing sample size. Some parameter estimates hit the lower bound of zero, but this is due to sampling fluctuation (as we illustrate in a small simulation study described in the Supplementary notes). Similar results were reported for other complex traits like intelligence (see e.g., Davies et al. 2011).
