100% BS.
Biologists absolutely define sex on a continuum or spectrum. Search around for some gender-bending examples. Start with banana slugs.
Turb-So what defines gender? Science usually views sex and gender as the same thing but society does not, sometimes. Is it chromosomal and hormonal like sex is determined in biology? Or is it genitalia? Because there are all sorts of mix and match going on there too. They are syndromes that are related to how we determine sex.
If you are looking for nice neat packages, this isn't the field.