Intelligence is actually way more complicated to measure than most physiological differences, such as baldness or eye color, because it's heavily impacted by things like gestational environment, nutrition, breastfeeding, or involved fatherhood.
Discussion
Studies with paternal twins suggest 50-80% genetic impact. There were some reports that this is primarily from the maternal side, but those were Fake News.
You're absolutely right, I was being vague but I believe what I said is generally correct, in a genetic sense. I was engaged to a paediatric nurse many years ago and you're absolutely correct in that gestation takes a major role. My long ago ex partner came home with some real horror stories of very young children born to mothers who'd neglected themselves and thus their unborn babies during pregnancy. So much so that I actually attended a funeral of one of those babies who had foetal alcohol syndrome, thar is no slight on the mother, these things happen but I've now genuinely got tears streaming down my face as I write this even though it was a long long time ago and the child in question was no relation...... Sorry, got a bit side tracked there, but I'd started to write so I thought I'd finish.