The narrow and broad heritabilities of each of these traits were estimated in a unified model. Five traits had significant X chromosome variance components either in males only (systolic blood pressure, adult height, triglycerides) or in both sexes (lipoprotein[a], whole blood serotonin). Interestingly, four traits had significant non-X sex interactions in which either the estimates of heritability were significantly different between males and females (LDL-cholesterol, FEV1:FVC) or the best-fitting heritability model was different between males and females (HDL-cholesterol, fat free mass). Thus, the genetic architecture of nine (of 19) common phenotypes had significant sex-specific genetic architecture. The best-fitting heritability model for six representative traits with sex-specific architecture is shown separately for males and females in Figure 4.
