From a post to DAVIDWEBER.NET forums on 1/10/12

Gene dominance among modified strains

TheMonster wrote:
namelessfly wrote:

    Sounds like a Typo to me. IIRC there was a conversation when Honor or her mom made the point that the genetic mods were dominant to ensure that children from interbreeding would have them.

    There was, and it has to be one of those couple of times DW just plain blew it. That's not what "dominant" means.

    A dominant gene is one that expresses its characteristics regardless of whether it is paired up with an identical gene on the other chromosome of the pair. For example, the gene for the Rh+ blood factor is dominant over the Rh- gene. A person with one Rh+ gene and one Rh- gene is positive for the Rh factor, but will pass that Rh+ gene along to only half their children on average.

    What DW has described as "dominant" would be as if an Rh+ sperm cell fertilizing an Rh- ovum would somehow search out the Rh- gene on the chromosome contributed by the mother, and replace it with an Rh+ gene, or that when the child with one of each gene starts producing sperm/ova, all of the Rh- cells would be discarded, and only Rh+ cells would get a chance to propagate to the next generation.

    And neither of those things happen. If someone had managed to figure out a way to do that, it would be entirely understandable if the rest of humanity resisted such tinkering and deliberately sought to eliminate "genies" from their midst. Send 'em off to Tau Ceti or something.

    (1) The specific passage in A Beautiful Friendship (taken from the final proofreading PDF) is: "And the modifications had been designed to be dominant, so that all her descendants would have them. But her kind of genie was perfectly inter-fertile [italics added for emphasis] with pure-strainers". That's exactly what I said in the original novella, and it's also we said in the novel.

    (2) The use of the term "dominant" indicates that the genetic modifications are "hardwired" into Stephanie's genotype, and that's precisely what they are. And, yes, they have figured out a way for a given bit of genetic code to "overwrite" itself into all of an individual's offspring… and it is part of the reason for the prejudice against genies. This isn't especially different from what Allison does as her "quick and dirty fix" for the Grayson genetic problem she discovers in Echoes of Honor, except that she uses nanotech in that instance rather than engineering a "search and destroy" genetic component, which is partly because of the prejudice against genies which came after the Final War, which substantially preceded the Meyerdahl first wave modifications. Stephanie uses the term "dominant" in her own thoughts, and it is used in at least one other place I know of in the books (I won't tell you where) in exactly the same way, because it's the shorthand way of describing the process.

    I find it a bit ironic that I get whacked by some people for getting too deeply into the hardware/tech/what-have-you, on the one hand, and that other people whack me for not giving enough detail about where the nanotech is, how the AI works, exactly how all of the genetic manipulation works, where I'm burying technology in the characters' automatically accepted background, etc. I did mean exactly what I said, even if the terminology the characters used may have been a shorthand reference developed/change/evolved during the intervening two millennia. (I might point out, for example, that in the eighteenth and nineteenth centuries when someone said "I doubt that's the truth" what they meant was "I believe that's the truth." Small shift in meaning over the last couple of centuries… as opposed to the twenty centuries or so which have passed in the Honorverse.)