Twin Research


Sex differences and non-additivity in the effects of genes on personality

Lindon J Eavesa1, Andrew C Heatha2, Michael C Nealea3, John K Hewitta4 and Nicholas G Martina5 c1

a1 Virginia Institute of Psychiatric and Behavioral Genetics, Richmond.

a2 Department of Psychiatry, Washington University, St Louis.

a3 Virginia Institute of Psychiatric and Behavioral Genetics, Richmond.

a4 Institute of Behavioral Genetics, University of Colorado, Boulder, USA.

a5 Queensland Institute of Medical Research, Brisbane, Australia.


New large-sample data show that non-additive genetic effects, probably epistatic interactions between loci, and sex-limited gene expression are significant features of the genetic architecture of human personality as measured by questionnaire scales of extraversion and neuroticism. Three large data sets – new data on large samples (n = 20 554) of US twins, their spouses, parents, siblings and children, correlations for Australian twins (n = 7 532), and previously published twin data from Finland (n = 14 288) – are subjected to an integrated analysis to test alternative hypotheses about the genetic causes of family resemblance in personality. When allowance is made for differences in reliability of the scales, the combined data are consistent with the same model for variation. There are significant amounts of genetic non-additivity for both dimensions of personality. The evidence favours additive × additive epistatic interactions rather than dominance. In the case of neuroticism, there is especially strong evidence of sex differences in genetic architecture favouring a greater relative contribution of non-additive genetic effects in males. The data confirm previous claims to find no major contribution of the shared environment of twins and siblings to these dimensions of personality. Correlations between spouses are zero, and the correlations for very large samples of siblings and non-identical twins do not differ significantly.

(Received May 05 1998)

(Accepted May 19 1998)


  • personality;
  • twins;
  • genetics;
  • sex differences;
  • non-additivity;
  • neuroticism


c1 Correspondence: Dr NG Martin, Queensland Institute of Medical Research, Post Office, Royal Brisbane Hospital, Brisbane 4029, Australia. Fax: + 61 7 3362 0101