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Mendelian magic inheritence - the plotline question

Discussion in 'Writing Discussions' started by wordwalker, Nov 22, 2012.

  1. wordwalker

    wordwalker Auror

    Since Thanksgiving's supposed to be about family, here's a puzzler that's been kicking around my head for a while:

    A lot of us define magical ability as an inherited trait, but at least one author has floated the idea that in her world it's a straightforward single-gene strongly dominant trait... and a sex-linked one, in that it's carried only on the female X chromosome. That would mean that (if we use the terms "witch" and "wizard," though note that the Harry Potter system is not this simple), combinations of offspring are:

    Wizard (Y X1) and "full" Witch (X1 X1) = 50% Wizard (Y X1), 50% full Witch (X1 X1).

    Mundane Man (Y X) and full Witch (X1 X1) = 50% Wizard (Y X1), 50% halfbreed Witch (X1 X).

    Wizard (Y X1) and Mundane Woman (X X) = 50% Mundane Man (Y X), 50% halfbreed Witch (X1 X).

    (And of course Mundane Man (Y X) and Mundane Woman (X X) = 50% Mundane Man (Y X), 50% Mundane Woman (X X).)

    but also because of those halfbreeds, there's also

    Wizard (Y X1) and halfbreed Witch (X1 X) = 25% Wizard (Y X1), 25% Mundane Man (Y X), 25% full Witch (X1 X1), 25% halfbreed Witch (X1 X).

    Mundane Man (Y X) and halfbreed Witch (X1 X) = 25% Wizard (Y X1), 25% Mundane Man (Y X), 25% halfbreed Witch (X1 X), 25% Mundane Woman (X X).

    And note, this is "strong dominance" so a halfbreed Witch is every bit as powerful as a full one, just less predictable in her offspring.

    (Some rules of thumb: a son simply has either one or the other of his mother's magic chromosomes. A Wizard's daughter is always at least halfbreed Witch, and a Mundane Man's daughter might be half Witch but no more.)

    (The magic has to be the X chromosome because a simple trait on the Y is too easy to predict. A Wizard's son is a Wizard, and everyone else is Mundane, yawn.)

    Now here's the question: what plotlines can we come up with about some of these combinations, in a society that either favors magical children or favors nonmagical (the effects aren't quite the same, since you can hide powers but probably can't fake them). Let's assume magical and other tests for magic and for genetics don't exist, because they'd make some of the complications we're looking for too clear. For example:

    • In a pro-magic culture, a Witch begins to fear her child is Mundane, meaning that not only the Witch but possibly some of her sisters are halfbreeds and therefore less marriageable -- also, if her husband is a Wizard, he can't be the child's father, but this is only certain if it's a daughter.
    • In an anti-magic culture, a secret Witch tells her children to hide their powers -- but since she's halfbreed and/or her husband is Mundane, some children are Mundane and grow up bullied by their magical siblings, and/or bullying them with threats of exposure.
    Devora likes this.
  2. Steerpike

    Steerpike Felis amatus Moderator

    What's the competitive advantage of being a woman with X X? Over time, why doesn't X1 displace X in the population? Those questions might give rise to some plot ideas.
  3. Twook00

    Twook00 Sage

    Is the magic straightforward for everyone? Like, the same spell can be used by all but some just put more oomph into it or can call it up easier? Or would each person have their own type of magic specific to them?

    It seems like magic would be used much like wealth/technology is in our society. Wealth/technology means power, and power does weird things to people. Some people have a lot of it, most have less, a few have none at all. This creates a heirarchy that can lead to lots of conflict.

    The first thing that popped into my head when reading this was a magically inclined society where those without magic are treated unequally and unfairly. It would be fun to tell a story where the protagonist has no magic at all in a setting where the vast majority does. I see it being very similar to the various racial issues we faced here in America (and frankly everywhere else).
  4. ascanius

    ascanius Inkling

    It's not that simple with regards to a wild type heterozygous sex linked trait for female, X1X. Both X chromosomes are not expressed, only one is. One of the X chromosomes is super-coiled into what is called a Barr body, that X chromosome is inactive, not expressed. That means that a female with XX1 there is a chance that X1 chromosome is not expressed, no magical ability. I don't remember what determines which is inactive, Wiki might know. That's one reason over time the X1 may not become dominant, there is no survival advantage to a non magic person.

    Sorry but i'm having trouble with your notation. Your counting phenotype; what is expressed, as genotype; what is present genetically. Your genotypes are correct, but...

    (YX) x (X1X1) = 50% Wizard and 50% Witch. If X1 is dominant and we are only looking at phenotype (what is expressed or whether or not they are able to use magic) then this combination will render a witch. X1 is domant to X so the X1 gene is expressed and not the X gene of the genotype. Your half breed witch has a dominant gene so is a full witch.

    Same, for this your going to get 50% witches for the same reasons above.

    For genotype your are correct. However the actual expressed results, Phenotype, are 25% Wizard, 25% mundane, 50% witch.

    Ok you got to it. I just dodn't get why you have halfbreed, the dominant gene is expressed so they would be a witch regardless of genotype.

    I just want to point out this completely ignores linkage, and the other complexities of genetics. For a base it works though.

    I think Inheritance issues would arise in a culture based off magic. Say somewhere along the line two recessive genes meet and produce a child with no ability to use magic even though both parents can. A YX1 x XX1. If said child is a prince or princess this would raise a very big problem, it could even be assumed that the child is illegitimate.

    Hell you could even have an entire plot line be a Mendelian analogy.
    Last edited: Nov 27, 2012
  5. wordwalker

    wordwalker Auror

    Fun, innit?

    Sorry about that; since I didn't put that reminder about what a halfbreed's phenotype is, I guess it wasn't clear that the descriptions I used were of phenotype and genotype both (in the case of witch genotypes, the only ones that needed distinctions).

    Oops, should have realized there'd be something like that, when males cover all those genes with only one X and female genes don't overload with the second. X-linked genes couldn't be the same as ordinary Mendelian genetics. :eek:

    Still fun though.

    Processes like this can apply to a magically-inclined society, which (as some people have said) would is what any society that had it would become-- unless the magic also carried a high cost, or if it demonized magic (that is, if magic were rare enough or fallible enough that they had a chance to). In the latter cases, you could have an anti-magic society where similar biases happen in reverse... except that you can hide powers better than you can fake them, so plotlines might take on different shapes.:)
  6. ascanius

    ascanius Inkling

    The Idea still works just don't have it sex based.
    What I think would be interesting is magical inheritance that is linked to another trait. For instance, people with red hair can use magic. You can take this a step further and use linkage to make people with red hair can use magic if they have green eyes also. I think the best one is to use something like what rabbits and certain species of cows have, I cannot remember what it is called. Anyway what happens is the extremities are colder and this affects the gene expression. So you could have a homozygous dominant person have the ability to use magic but a homozygous recessive is unable to, then a heterozygous dominant would only be able to use magic with the extremities (this would depend on the magic system too though).

    Back to the question. There are a lot of good ideas that can stem from this one idea. I think most would center around acceptance into society or groups based on magic ability and the fall out when pedigree beliefs are found to be wrong. Like took00 and you have already said.

    Star crossed lovers anyone? You could have a society where pedigree is very important and magical families rule and force their children to marry those with the right pedegrees.
  7. keiani

    keiani Dreamer

    Cool idea! Hmmm, in a pro-magic society, you can always focus on a family who ignored their first mundane child in favor of later, magical children.

    Also, people uniformed about genetics could doubt that a Witch and a Wizard could have a mundane child, and therefore shame the Witch by assuming the child's father is someone else? (I'm remembering a brunette couple I read about somewhere who had trouble with family members who didn't believe it was possible for them to have a blonde baby.)
  8. Zireael

    Zireael Troubadour

    I agree about uninformed people. I remember reading or hearing about a case of a black-skinned child being born to white parents, because a) there was a mutation b) they both had African ancestors way back the line.

    On topic: I use Mendelian genetics for determining the strength of blood powers in my world. So knowing some genetics is certainly useful.

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