In contrast, the default model predicts that the correlation between the genotype and sexual orientation should remain unaffected when gender nonconformity is entered into the path model. The path analysis presented here is based on the fact that monozygotic twins will be more similar than dizygotic twins on any trait with non-zero heritability. Accordingly, the unit of analysis here is the twin pair, and each variable is a measure of the pair's similarity on the three variables at issue. A twin registry study of sexual orientation. A genetic study of male sexual orientation.
Heritable factors influence sexual orientation in women.
The subtlety of sex-atypicality. A linkage between DNA markers on the X chromosome and male sexual orientation.