However, genes vary greatly in size and when we considered the length of genes we observed that the estimate of hC2 for height and QTi was also proportional to the total length of genes on each chromosome (Lg(C)) where gene length is defined as physical distance between the beginning and end of UTRs (Supplementary Fig. 4). Since the correlation between LC and Lg(C) is extremely high (r = 0.97), we were unable to discriminate whether LC or Lg(C) is causative by multiple regression, i.e. the regression of hC2 on LC is not significant fitted after Lg(C) and vice versa (Supplementary Table 3). Therefore, a different analysis was required. We asked whether we could still observe a significant regression of hC2 on Lg(C) when chromosome length was held constant. We implemented this by dividing the genome into segments with the same length of 50 or 30 Mb and then estimated the variance explained by each segment ( hS2) in a joint analysis (Online Methods). We found that the regression of hS2 on the total gene length per segment (Lg(S)) remained significant
