if someone were to try to create a Neanderthal a few years from now, starting with ancient DNA, they’d have to have worry a lot about data errors, because such errors would translate into mutations, which might be harmful or even lethal. Assume that we have figured out how to get the gene expression right, have all the proper methylation etc: we have modern humans as a template and you know there isn’t that much difference.
They might try consensus averaging – take three high-quality Neanderthal genomes and make your synthetic genome by majority rule: we ignore a nucleotide change in one genome if it’s not there in the other two. ‘tell me three times’, a simple form of error-correcting code.
But doing this would cause a problem. Can you see what the problem is?