Recent findings have challenged the dogma that gonadal hormones are the sole factor mediating sexual differentiation of the mammalian brain, and have highlighted the importance of sex-linked genes in this process, either independently, or in combination with, gonadal hormones. Using two rodent models, this thesis investigated the roles of the Y-linked (male-specific) gene Sry and other sex chromosome-linked genes on emotional behaviour. Using an established murine ‘four core genotype’ (FCG) model an attempt was made to dissociate, ‘Sry-dependent effects’ (due to direct effects of Sry brain expression, or to downstream hormonal factors) and effects due to ‘sex chromosome complement’ (i.e. sex-linked genes other than Sry). The mouse work was augmented by the development of a novel rat Sry antisense ‘knockdown’ model permitting investigation of the behavioural effects of direct manipulation of Sry expressed in discrete brain areas.