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Of course, there won't be a precise known answer to the question, as it is not even known precisely what percentage of the genome is functional in the first place - but I am still looking for research.

The book "Principles of Neural Design" claims that "20% of our genome is devoted to coding neural signaling molecules". This seems not only vague, but also suspect to me, as that is more than the fraction of DNA that is known to have a function in the first place - maybe they meant only protein-coding genes?

One hears a lot about the human brain as "the most complicated object in the universe" etc., but I would like to put a number of that and compare the genetic complexity needed to express it to that needed for other body parts.

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  • $\begingroup$ The complexity of the brain is not necessarily related to the amount of genome involved. Humans have much more complex brains than rodents and yet mostly share the same proteins with only relatively minor modifications. $\endgroup$ – Bryan Krause Mar 12 '20 at 15:46
  • $\begingroup$ I think that depends on the definition of "complexity". In terms of "amount of data needed to describe an instance of the system", I agree - but then, counting the degrees of freedom, a rock could have a higher complexity than a human brain. What I was getting at is "amount of data needed to recreate the system" (further restricting to "biological data", not the experiences the brain bases its learning on or randomness), and if the human brain doesn't need much more "code" than a mouse brain, these would indeed be similar according to the definition I am interested in. $\endgroup$ – streawkceur Mar 12 '20 at 16:55
  • $\begingroup$ I agree with your assessment of that statement as vague. At best, it's a gross oversimplification. For one thing, neurotransmitters are not directly encoded by genes. However, this online fact-sheet published by the NIH state, "at least a third of the genes in the human genome are primarily expressed in the brain." Still a bit vague, but slightly less so. Obviously not a proper answer, hence the comment format. ninds.nih.gov/Disorders/Patient-Caregiver-Education/… $\endgroup$ – MikeyC Mar 13 '20 at 21:07

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