In biological terms, it would be female/male, gonadally. But it's far more complex than that, because the sexual organs don't always develop the same and there are hormonal and genetic aspects to sex that may be different. Even brain structure plays a part. But in social terms, when referring to gender, it depends on how they present and what they identify as. Consider what I had stated before: without checking a person's genitals, performing a genetic or hormonal test, you just don't know (and I do recognize that you stated you would use their preferred terms). A person could have all the biological markers of male or female, or a mix of these (genetically female but gonadally and hormonally male), but present socially as different.
One of the things about biology as a science is, it's messy. It's not quite as black and white as other sciences.