It's true that genes and proteins is nothing like code, but in the context of understanding the brain, I think that should be cause for optimism, because it means that nature has its hands tied behind its back. The genes can't just contain a description of how the brain should be wired together, because the description also has to be "self-executing"; the entire object must robustly self-assemble just from proteins physically interacting. So although 700 megabytes of mouse genes could potentially contain a lot of stuff, it might be possible to do the same thing much more simply if we can program a digital computer instead.
Like, the connectome for C. elegans has been mapped out; it's can be written down as a 2 megabyte ascii text file. Just the connectivity is not enough to actually reproduce the behavior of the worm, you would also need data about the weight of each connection, but it's still a lot less data than the worm genome (about 25 megabytes---I hope I got the number right this time!). The worm genes also need to contain a lot of additional stuff to build functioning cells internals, etc, stuff which hopefully is irrelevant to the actual cognition.
Like, the connectome for C. elegans has been mapped out; it's can be written down as a 2 megabyte ascii text file. Just the connectivity is not enough to actually reproduce the behavior of the worm, you would also need data about the weight of each connection, but it's still a lot less data than the worm genome (about 25 megabytes---I hope I got the number right this time!). The worm genes also need to contain a lot of additional stuff to build functioning cells internals, etc, stuff which hopefully is irrelevant to the actual cognition.