Partitioning the genetic variance into the 22 autosomes revealed that the phenotypic variance of extraversion explained by each chromosome is proportional to its length (R2=0.20, P<0.05; Figure 2). This corroborates evidence of a polygenic model underlying variation in extraversion. As longer chromosomes harbour more genes, a linear relationship between length of a chromosome and the estimate of variance explained by that chromosome is consistent with the hypothesis that many genes of small effect contribute to genetic variation of the trait. The s.e. of the estimates for the chromosomes were high so that none of the estimates differed significantly from the regression line. This suggests that no individual loci disproportionately affect genetic variation. Genome partitioning for neuroticism did not show a significant relationship between chromosome length and variance explained (Figure 2). This is not unexpected given the smaller genetic variance that can be attributed to common SNPs.
