The difference between gender, your sex and sexuality
Gender is about who you are and the way you behave and identify with other people. This can also be influenced by other people's expectations of you. For example people expect you to behave differently if you are a man or woman, boy or a girl. Most people identify as the gender usually associated with their biological sex. Some people do not, and sometimes these people may identify as trans, transexual, transgender or genderqueer.
Sex refers to our biological differences; chromosomes, hormonal profiles, internal and external sex organs. Some people can and do choose to alter these biological differences, transexuals for example.
Sexuality is defined by who you are sexually and romantically attracted to, so that could mean lesbian, gay, bisexual or heterosexual.
