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One of my characters has a genetic disease called "Complete Melanism". Her eyes, her skin, her hair, and her internal organs are all black. Like a famous Indonesian breed of chicken.

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The allele involved is a mutation of the MC1R gene found on chromosome 16. The mode of inheritance is incomplete dominance. If we have one allele, only our external body is black, if we have two alleles, both our external body and our internal body is black.

My character is of European descent. Her paternal grandfather is Romanian, her paternal grandmother is Dutch, her maternal grandfather is Scottish, and her maternal grandmother is Greek.

I wonder is my genetic disease realistic or a total fiction?

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    $\begingroup$ There's just so much wrong with this question .. I haven't got the time to pick through it all so I'll just focus on one item and leave the rest for others .. any mutation is only a disease if it's demonstrably detrimental to the organism, so what are you trying to say? that dark pigmentation is inherently bad? why would you think that? $\endgroup$
    – Pelinore
    Dec 8, 2022 at 2:28
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    $\begingroup$ Bit uncalled-for, it may just have been inaccurate word selection, thinking that "genetic disease" describes any genetic peculiarity. (From the rather pedantically detailed gender label, it looks like OP is in fact particularly attentive to "identity" questions and like they're going to be a theme in the series). But yes, if it doesn't cause the character any other difficulties and just looks different, it's called a "genetic condition" or a "genetic mutation" - "genetic disease" and "genetic disorder" are only for things that make you ill. $\endgroup$
    – A. B.
    Dec 8, 2022 at 4:26
  • $\begingroup$ Verifying that the internal organs are also black could have a harmful effect on the person's life which might make the story much shorter than needed. While the person is still living, they might simply look like someone from Sudan. $\endgroup$
    – David R
    Dec 8, 2022 at 15:42
  • $\begingroup$ @DavidR It would be easy enough in the story to do something like have her appendix removed - a common enough surgery - to "discover" the coloration. $\endgroup$
    – JBH
    Dec 8, 2022 at 16:24
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    $\begingroup$ If her bones are black (as happens with the chickens), her teeth might be black too. $\endgroup$
    – A. B.
    Dec 9, 2022 at 5:58

4 Answers 4

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Sometimes, trying to be realistic is a useless distraction

To answer your question, it's 100% fiction.

Given the background you provided, I wonder why you need a "realistic detail" like the specific genetic condition that would lead to a person named Black Black having both black skin and black organs. From my perspective as one who operated a micro-publisher for ten years, you're really belaboring the point. Unless the primary point of your story is about the genetic condition (which I'm seriously doubting), it's a distraction from your message.

But, let's try a little worldbuilding and let you worry about your story.

Fibromelanosis

That "famous Indonesian chicken" you mentioned is the Ayam Cemani. Black feathers, black comb, black beak, and either black or grey muscles and internal organs. Some of the chicken varieties that share the Ayam Cemani's genetic circumstances even have black bones. Science calls the genetic combination that has this result fibromelanosis, and there's an important point to be made before we continue:

The genetic basis of fibromelanosis remains unclear. (Source)

That's why your idea is 100% fiction. We're not sure what causes the color of the chicken's internal organs. We certainly don't know what might cause a similar coloration in humans. So what we're looking for is an explanation that meets suspension of disbelief.

From that same source I quoted above we learn,

The results showed that L-dopachrometautomerase precursor (DCT), tyrosine aminotransferase (TAT), 4-hydroxyphenylpyruvate dioxygenase (HPD) from the tyrosine metabolism pathway, coagulation factor II (F2), fibrinogen beta chain (FGB), plasminogen (PLG) and complement component 7 (C7) from the complement and coagulation cascades were important genes in the fibromelanosis process in black-bone chickens. These candidate genes require further correlation analysis and functional verification.

This comes from an abstract. I don't have access to the full article. I don't know if any of the genes mentioned exist in humans. But none of them are the MC1R gene you mention. The MC1R gene does exist in chickens, and yet isn't a candidate for fibromelanosis. Thus, I'd abandon the MC1R gene.

But what's important is that what the authors of that article said means nothing to me. It would mean nothing to 99.999% of your readers. That's why trying to be realistic can be a distraction. While everyone's trying to figure out what you're talking about, they're forgetting the message you're hoping they'll remember.

So I recommend you avoid your invented genetic condition and stick with fibromelanosis. It has a basis in reality, which lends credibility to the conditions of your story, which is what you're really looking for.

In 2032 a young woman was born with a rare genetic condition. Researchers called it "human fibromelanosis." Not knowing how acutely germane her name would be, her parents looked down upon their perfect baby, and named her Mélanie Negru.

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If both her parents are white, the maths doesn't add up

You say that Mélanie's grandparents are all European. Of course, nationality doesn't prove anything about their colouring, they could be black people living in Europe, but the fact that you mentioned it sounds like you possibly mean that they're white.

In that case, if having one copy of the gene caused dark skin, none of Mélanie's grandparents could have had it, leaving nobody for Mélanie to inherit it from. For Mélanie to have two copies of the gene, each of her parents would have had to have at least one copy, and thus according to what you described they would both have dark skin.

Their dark skin would have to be caused by a different gene or genes from what normally causes dark skin in people of African descent, since there seem to be no known cases of black-inside-and-outside humans in reality. They could, of course, have this fictional mutation and also coincidentally be black in the usual way, but if not, if they're people of European descent but have black skin, then both sides of Mélanie's family would be well aware that their genetics were a bit unusual long before their daughter was born.

I'm not sure what you have planned, so this may work. But if not, if what you're trying to get is a baby that's black inside and outside born unexpectedly to two white people, then it seems like what you need is a recessive gene. That way, one copy does nothing, two copies lead to what Mélanie has.

(Note that, according to Wikipedia, what the Ayam Cemani chickens have is a dominant gene, so what Mélanie has can't be exactly the same mutation that the chickens have unless one of her parents is like that too. But, as JBH's answer points out, apparently nobody's sure exactly what mutation the chickens have anyway).

If her parents were both white, naming her "Mélanie" might be considered a bit tactless of them - it makes it sound as if they think her weird genetic condition is the most important thing about her. That might be intentional on your part, though!

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    $\begingroup$ What you've said is true unless one of the following took place: (a) the mutation was caused by an environmental trigger such as pollution and therefore was not inherited from the parents, or (b) her parents possessed the trait but it was not expressed. There are a number of genes which regulate melanogenesis and melanocyte differentiation, any of which may be turned off. $\endgroup$
    – Theresa Kay
    Dec 8, 2022 at 5:36
  • $\begingroup$ Thanks, thought there might be something I'd overlooked, so many possible complications. Spontaneous mutations seem to happen more often than you might think. $\endgroup$
    – A. B.
    Dec 8, 2022 at 6:05
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    $\begingroup$ Not one but two spontaneous mutations providing the necessery two copies of the gene described would be a rather unlikely occurrence however 😉 $\endgroup$
    – Pelinore
    Dec 8, 2022 at 13:21
  • $\begingroup$ @Pelinore that’s a good point. I forgot that the dominance is incomplete. In that case, regulation of gene expression is a more plausible explanation. $\endgroup$
    – Theresa Kay
    Dec 8, 2022 at 18:30
  • $\begingroup$ @TheresaKay its not (entirely) 'impossible' for the same mutation to occur in both copies of a gene as described by the questions OP now in his edit, very little is, but the odds are astronomical, its probably equivalent to something silly like randomly rolling 6 on a dice all day. $\endgroup$
    – Pelinore
    Dec 8, 2022 at 22:33
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If we have one allele, only our external body is black, if we have two alleles, both our external body and our internal body is black.

As @A. B. and others have pointed out, due to the dominant nature of this gene, the protagonist’s parents would have each had to possess one allele, which they passed on to their offspring. If neither expresses black skin, this is hardly a plausible genetic condition.

Several solutions to this conundrum:

1. Switch the pattern of dominance.

If a person has one allele, only their internal organs are black. If they have two alleles, both their external body and their internal body are black.

This is, in my opinion, the easiest solution. Both Melanie’s parents have one allele of the gene. However, since this only causes internal organs to be black, neither of them express black skin. They may not even know that their organs are black. This allele could have been passed through her European ancestors for generations before she received two alleles, expressing not just the internal phenotype but the external black skin as well.

2. Regulation of gene expression.

As I suggested in the comments, gene expression could explain this discrepancy. Leave the alleles as is. Both Melanie’s parents possessed one allele of the trait, but it was not expressed. There are a number of genes which regulate melanogenesis and melanocyte differentiation, any of which may be turned off. In Melanie, these genes were turned on (could be due to any number of reasons), so she expressed the phenotype while her parents didn’t.

3. Environmental factors were involved.

The mutation was not inherited from her parents, but was caused by an environmental trigger such as pollution. This is in fact a plausible explanation for spontaneous generation of melanism.

See Wikipedia:

Industrial melanism is an evolutionary effect prominent in several arthropods, where dark pigmentation (melanism) has evolved in an environment affected by industrial pollution, including sulphur dioxide gas and dark soot deposits.

Of course, as @Pelinore pointed out, the likelihood of this mutation randomly occurring twice, to mutate both alleles, is considerably less likely than one mutation. If you want to stick to your incomplete dominance explanation (and not complete dominance, in which one allele is sufficient to express the mutation), this explanation may not be plausible.

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Yes

You have answered your own question.

If we have one allele, only our external body is black, if we have two alleles, both our external body and our internal body is black.

So give her two alleles. Then she will be black inside and out like an Ayam Cemani chicken.

Since all four grandparents need the allele to pass it on, they will not look like typical Romanian/Greek/Scottish/Dutch people.

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