How to uncheck boxes in "gender/sex" field?

I added an extra category (transgender) to the gender/sex menu by going to "Settings", then "Predefined Values", then "Sex" from the dropdown list. I then typed in "transgender" in the following boxes: Value, LKey, Lkey2. But when I go to browse profiles, "male" and "female" both Automatically have checks next to them already (checkbox checked) and transgender doesnt. How can I uncheck the male and female boxes, so the person has to check which box they are, instead of both already being checked. If it isnt possible to uncheck them, is there a way to check the transgender box so it doesnt look like only the male and female boxes are checked and the transgender isnt?