Nouns and verbs have gender. Gender is a grammatical term. They are masculine, feminine, or neuter.
Men and women, boys and girls have sex. They are either male or female.
Hope that helps, too.
The use of the term Gender for Sex is very deliberate.
It is used to give lie to the idea that our being male or female is a social constrict ( is that the word) that should and can be changeable according to our own self view. It says that being male or female is not determined by biology or in how we were created by God but by our culture. As such we are the ones who determine if we want to live as a man or as a woman.
If sex is not a product of God's own creative will its physical expression can no longer be limited to the Biblical and/or traditional moral view. But all forms of physical expression are valid since their very validity comes from our selves.