chromosome (Ng(C)) for height and QTi (Supplementary Table 3). Since LC and Ng(C) are correlated (r = 0.628), we performed a multiple regression analysis of the estimate of hC2 on LC and Ng(C), and fitted models in which chromosome length was fitted after the number of genes and vice versa. When including both LC and Ng(C) in the regression model, Ng(C) was not significant and LC was still significant for height and QTi (Supplementary Table 3). The regression of the estimate of hC2 on either LC or Ng(C) was not significant for BMI and vWF. These results are consistent with variance explained by each chromosome for height and QTi (but less so for BMI and vWF) being proportional to the proportion of the genome being considered. Although longer chromosomes harbour more genes that are implicated in abnormal growth or skeletal development, the relationship between variance explained for height and chromosome length remains significant after fitting the number of such genes (Supplementary Fig. 1). We provide evidence that the linear relationship between the estimate of hC2 and LC cannot be attributed to the fact that longer chromosomes have more SNPs and thereby smaller sampling errors when estimating genetic relationships between individuals
