I got the phrase “sex is genetic; gender is cultural” from The Feminist Files, by a student from North Carolina inspired to make a difference in the world. Apart from in grammar, I had not previously understood the use of the word gender and I am grateful.
My caveats: I am the one who gets to say what sex I am, and the sex I have been at all times in my life. I am and have been female. “Sex is physical, gender is cultural” would be more assonant; sex is physical, involving brain structure and genes as well as gonads.
And gender is a cultural phenomenon in that it is my cultural expression of something innate. Had I had two X chromosomes and a male outward appearance, if gender were merely cultural I would have grown up happily male, conformed to my upbringing, expressing maleness culturally as my society and family expected, more or less. There is something there in me which I express culturally, something “feminine”. I like flowery skirts, crystal pendants and long, dangly earrings.
Feminism here has won the campaigns to get women rights to go to university and vote, and is winning equal respect at work. It can now be in part about acceptance of the widest range of cultural expression of gender, liberating people to choose to express ourselves however we wish, neutrois and gynandrous as well as all aspects of male and female.