Comment by gwern | Hacker News Reader

Comment by gwern | Hacker News Reader

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I've idly wondered how you could interpret all the mutations in X-Men, but I don't know enough about the families or inheritance to make any reasonable guesses (I've seen a few cartoons and movies and that's about it). I know mutants generally have mutant kids but don't the powers differ? Which doesn't make much sense and I can't retcon it.

I have noticed, however, that in _My Little Pony_ (which I've finally gotten around to watching), it seems like earth/pegasus/unicorn traits are not races or subspecies analogous to human races but instead likely follow a polytomous liability threshold pattern. Why? Because we see the Cakes, two earth ponies, manage to have a pair of pegasus and unicorn fraternal twins, and when queried, mention they have some pegasus/unicorn ancestry. Since the pony type is mutually exclusive (we never see any pony who is both pegasus and unicorn, aside from the alicorns who are special magically-created cases), I don't know of any kind of common Mendelian trait pattern which would give a single type, normally breed true, and allow two earth pony parents with mixed ancestry to have kids who are both unicorns and pegasi (one non-earth-pony offspring would be fine as it would simply indicate a recessive discrete trait, but two different others? I don't see how that works unless you postulate some sort of multi-locus Mendelian trait with dominance of earth trait by both unicorn and pegasus, I guess?). Whereas if it's polytomous liability threshold, then that would be possible albeit unlikely, since they could inherit different fractions of ancestry and get pushed across different type thresholds.

Mendelian ponies could have a single gene with 3 alleles, E/U/P, with EE, EU and EP earth, UU and PP respectively unicorn and pegasus and UP either unicorn or pegasus at random (i.e. depending on other genes). If the two parents are EU and EP they are earth but offspring of all three types is possible. An even simpler model: one gene with two alleles, earth and fancy, earth dominant, fancy ponies become unicorns or pegasi depending on rainbow intensity or other non-genetic factors.

In the Dune case a very Mendelian concern with preserving a few important mutations in very narrow bloodlines could be combined with a secondary requirement for high IQ, physical fitness etc. that could be (inefficiently) satisfied by focusing on "well bred" aristocracy that benefits from marrying genetically far above average people.

I feel stupid saying this, but it was explained to me as being like light through a filter, like for spider man, Parker was always going to get powers (all things being equal) but because the trigger was spider related the powers \ way he manifests them are "spider colored", like light through a keyhole, different keyhole, different image, but same light source.

With regard to the X-Men, I think they imply the "present day" is a Cambrian explosion, that then settles down in the far future into the most useful powers becoming common if less godlike levels: immortality, psi, telekinesis, and any other boring wish fulfillment.

As far as the X-Men go, very often children have similar (if not enhanced) powers compared to their parents c.f. Jean Grey and her multiple-universe-spanning offspring with some variation on tele{pathy,kinesis}.

However, in the cases where the mutation seems to not be directly inherited, the explanation lies in the "implementation details", as it were. When the X-gene activates (due to puberty, stress, etc.), it releases a protein that goes on to cause mutations in surrounding genes, seemingly at-random but not so random that you have "mutant" teens dropping dead of sudden protein deficiencies.

Why not two traits? One that determines if (Earth || !Earth) (call it the "Magic" gene) and one that determines (Pegasus || Unicorn) but only if the other gene is active.

I don't really like some of the mechanisms like dominance because it implies something for which we have no canon evidence: biases in discordant offspring towards particular types. And requires some rather specific patterns: in that case, it would require Mr and Mrs Cake to both have exactly 1 Earth/!Earth allele pair (so they become Earth but have a !Earth which can be passed on) and then each has a different Pegasus or Unicorn allele, which then also separately get passed on so they have two kids with !Earth/Pegasus and !Earth/Unicorn pairs. And it seems like if that were how it worked, you would expect way more discordant families to show up. (While polytomous threshold model can accommodate any level of rarity or stochasticness quite easily and naturally.)

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