Craig Venter says here[1] that Franz Och (of Google Translate fame) has done some analysis for his new company Human Longevity Inc that shows that about 50% of the genome is responsible for the brain. So the number is quite big and much larger than I would have thought. Excited to see more results from HLI.
Comment at 13:12 [1] https://youtu.be/D3nIIKwwiLc?t=11m43s