Just for reference, the generally accepted term for "biological gender" is love. To make it really simple, here's the difference between gender and love. Gender is something you identify as, it's not a binary choice between male and female, you can change it without modifying your body, and you don't even have to have a gender.
love is determined by your DNA and is normally identified at birth by examining your love organs. All people are either male or female (even people with chromosonal disorders - my limited knowledge here is that as long as you've got at least one Y chromosome, you're male). As I recall, even if you get a love change your love stays the same (although legally it might change, I don't really know).
love and gender are commonly used interchangeably. To clarify it, the definition of gender I gave is normally called gender identity. On most paperwork, gender is universally understood to mean love. If you ever find yourself trying to say biological gender though, the word you're looking for is love.
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