Our analytical approach considers all observed or estimated genotypes (rather than focusing on alleles transmitted from heterozygous parents) and thus is not immune to effects of population stratification. In homogenous populations, this type of analysis is expected to be more powerful (50, 51). To adjust for the effects of population structure and cryptic relatedness among sampled individuals, we used the genomic control method to adjust our test statistics for each trait separately (52). We checked the genomic control value for our genome-wide association analyses (52), and carried out principal component analysis of genome-wide SNP data in a subset of unrelated individuals (53). Neither analysis suggested evidence for population substructure or genetic outliers in the sample.
