My mother was a lover of alcohol and I've turned out alright. I'm no genius, but who is? I disagree that IQs are particularly useful since there are so many types of intelligence and as a species I don't think we've actually pinpointed what intelligence is and how to measure it, let alone different variations of it.
However, that's probably bias on my part since I have always performed badly on them. I can do most linguistics questions fine, but arithmetic, spatial awareness and non-verbal reasoning are not my forte and I end up with a below average IQ. I failed my 11+ miserably, and although I did well in my GCSEs I think I only got good grades because of my ability to write rather than know anything (hence my lowest grade in Maths, where I couldn't write my way out of a situation).
I think there is a huge hereditary factor involved. My grandfather died when I was four, but all accounts of him seem to point to the suggestion that he was a highly gifted man. Despite the fact he left school very early on (and he had been to a very rubbish school in one of the most deprived areas of East London) because he couldn't afford his school uniform, he managed to teach himself to play huge numbers of instruments; write letters not just competently but lingusitically astute or passionate depending on the situation; and had a vast knowledge gleaned from access to the public library. However he had been a labourer his whole life with no intellectual stimulation from other people (his wife was, shall we say, of limited intellect). Knowing this makes me think that even people who have grown up in dire environments will eventually, if not prodigiously, reveal their gift(s). None of his children went to University because of the same reason, but out of eight grandchildren they have all done exceptionally well academically and a number have gone to Oxbridge/St.George's; the others I'm sure were of the calibre to go but chose not to.
At the same time, I think nurture can help in bringing a gift out early on, e.g. in reading to your child, which can ultimately aid in success but not necessarily intellectual proess later on.
Most "geniuses" aren't born reading the Encyclopaedia Britannica: in the case of most, it takes until adulthood before their full potential is realised (an exception being Picasso). You can get an average ability pupil through any exam with sufficient tutoring and work, but as soon as they are posed with a task that requires thought, their lack of intelligence will become evident. In that respect, I think intelligence is rather (unfortunate for some) finite and there's not a lot you can do about it.