I agree with Jim here. There’s nothing implausible about Spock, if we make the assumption that Spock’s genome was built from the ground up. No, Spock was not an accidental child; the odds of Vulcans and humans having compatible genetic code is only slightly less than the odds of me and Jim McCain growing more hair on our heads, which is to say not at all.
I assume that Spock is either genetically fully human or fully Vulcan. Assuming the latter, I believe Amanda’s DNA was decoded, then rewritten as the Vulcan DNA-equivalent, then matched with Sarek’s DNA. Some human genes aren’t going to have Vulcan analogues, and likewise some Vulcan genes won’t be represented in the human genome. But overall, Spock does carry genetic traits from both sides of his heritage, but he doesn’t actually carry human DNA.
It’s a tricky concept, but it’s what I believe. Some might say that the scene of Spock’s birth in Star Trek V is impossible under this scenario. Again, I say that it is possible; when designing Spock’s genome, I think the genetic coding for a human placenta could have been done, and then Amanda was given drugs to prevent her body from rejecting Spock.
Spock, poster-child for the ultimate in test-tube babies.