Aggressive behaviour: contributions from genes on the Y chromosome.

The Y-linked gene SRY initiates male development in mammals through a pathway of gene activity leading to testis development. The testis then exports the male signal to the rest of the embryo via secreted molecules such as testosterone. These subsequently lead to many male characteristics in terms of anatomy, physiology and behaviour. Because males tend to be more aggressive than females, and androgens are often blamed for this, SRY can be thought of as a contributor to such behaviour. However, any effect the gene has is very indirect. Nevertheless, accumulating evidence suggests that other sex-linked genes may have more direct effects on differences between the sexes, and some of these are likely to include behavioural phenotypes. While it is not yet clear how important these are, they could compound decisions when treating cases of sex reversal and intersex conditions. They should also be borne in mind as a source of genetic variation when looking at differences between individuals, including behavioural traits such as aggression.