ok, i'll explain this the best i can.
Admin>builders>field builder then look for box that defines sex, its actually from a predefined list.
click on the block that says sex untill it opens up, (eyop this is getting smutty LOL ) Go to advanced in the block tabs and you will see a link that says sex, click on that and you will get a box with the values already there. Male female. Now click on the big green cross and this will give you an empty space to fill in. Ive added couples in here by following the examples that are already there. Save and when you go back to the drop down menu, it will show the field you just put in.
Im sure there is a easy way to do this, but this works.
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Regards
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Tyke