Ask a Scientist: X-Men Edition

Could the X-Gene exist in real life?

By: Katherine Hill and Sienna Schaeffer
Edited by: Madeline Nicol

Image Credit: Marvel

Welcome to the exciting new column where you send us the science and science-adjacent questions that you’ve always been too afraid to ask and we find experts who can answer them!

I don’t know how familiar you are with the X-Men, but their origin story is that they all have a mutant version of the same gene that gives them their powers. It seems like the same mutation should have the same effect in everyone, but the X-men’s powers range from growing a pair of wings to telepathy to shooting lasers out of their eyes. My question is whether the same mutation could really have such a wide variety of effects in different people.

Submitted by: Hank M.

The short answer is no, but that doesn’t go very far toward meeting our word count so here’s the long answer.

As you so eloquently stated, the origin story of the X-men says that they all share the same mutation that leads to this bewildering display of phenotypes. In order to evaluate the legitimacy of this claim, we should start by talking about its most basic assumption: the X-gene is actually a gene (in the comics, obviously it’s not a gene out here). More specifically, is the X-gene actually heritable? You didn’t actually ask that question, but I think it’s an interesting question, so we are going to talk about it anyway.

Before we get into whether or not the X-gene is heritable or not, let’s set down a little bit of terminology. I know it’s no fun, but it will be over soon. First, there’s an important distinction between genotype and phenotype. Genotype is the physical version, or allele, of a gene that you have. In this case, there would be two possible alleles: a normal* or mutant X-gene. Phenotype is the actual effect that that gene causes (e.g. eye color or wings). For example, yours truly has blue eyes. My phenotype is blue eyes and my genotype would be two alleles for blue eyes. Two? Yes. Read on.

Everyone inherits two copies of every gene: one from your mother and one from your father. If you only need one copy of an allele to produce the related phenotype (e.g. the gene for brown eyes), then that allele is dominant. If you need two copies of an allele to produce the related phenotype (e.g. the gene for blue eyes), then the allele is recessive. For example, my cousin and her children all have brown eyes because they all have two copies of the brown allele. My father has brown eyes because he has one brown allele and one blue. Again, I have blue eyes because I have two copies of the blue allele. I think you get it so we can be done talking about my family’s eye coloring.

What does this have to do with heritability? If the X-gene is actually heritable, it should have an inheritance pattern that we can figure out based on our understanding of dominant/recessive genes.** So, does the X-gene follow a dominant or recessive pattern? When geneticists want to find the inheritance pattern for a gene, they do something called a pedigree analysis. This means that they find a family that has a large number of people that express the trait that they are interested in, be that sickle cell anemia or superpowers, and look for patterns.

Luckily, with 50+ years of comics and some extremely obsessive fans, there’s a trove of data available for us to build our pedigree with. First, let’s look at the parents of the X-Men. For the most part, X-parents do not appear to have superpowers themselves. This would suggest that the X-gene is recessive. Both parents carry one mutant and one normal copy of the gene, but are themselves normal. The X-Men then inherit a mutant copy from each parent, meaning that they have two mutant copies of the gene and express the recessive trait.

X-pedigree (M = normal allele, m = mutant allele)

What about the X-children? If the gene is recessive, then all of the children with two X-Men parents should also have superpowers because the X-Men only have mutant genes to pass on to their children. In fact, this is exactly what we see. For a simplified X-pedigree, see the figure to the left.

So, as far as we can tell, the X-gene is heritable and behaves like a real-life gene. So far, so sciencey. So what’s the problem with this gene? Actually, there are two problems. First, leaving aside the question of whether one gene could cause all of the X-Men’s different superpowers, could one gene cause even one superpower? Because of how complex each superpower is, the answer is probably no.

According to Dr. Robert Brooker, a professor of genetics, cell biology and development, “It’s in the land of outrageously unlikely that a single mutation could produce people with the X-men qualities. For example, at least hundreds of genes (maybe thousands) are involved in the development of wings.”

Essentially, there is no way that one gene could carry all of the information necessary to tell the body how to create a functioning pair of wings. Instead, hundreds of genes work together. Some genes determine where the wings should go, some genes determine how they are shaped, many more are involved in feather formation, and so on. Other complex traits, like eyes, skin color and (probably) telepathy, are formed in a similar way. I’m not sure how many genes are involved in shooting lasers out of your eyes, but I’m willing to bet that it’s a lot.

Is there any way that one gene could have such a major effect? Dr. William Oetting, a professor of experimental and clinical pharmacology told us that the answer is probably yes, but in the wrong direction. “There’s a lot of ways of making things go bad… but making someone supernormal, whether you’re looking at IQ or athleticism or anything like that, is typically not going to be one gene.”

The problem is that it is generally much easier to make something go wrong by changing a gene than it is to make something go right. Dr. Oetting explained that knocking out one important gene could lead to a decrease of 60 IQ points, but increasing IQ by the same amount above average would probably require changes to at least 200 genes.

Getting to the question that you actually asked though, assuming that there was a gene that could cause superpowers, would it be possible for that gene to cause such a wide range of superpowers in different people?

Dr. Oetting brought up the example of Waardenburg syndrome, whose symptoms can include a white forelock of hair, widely spaced eyes, patchy pigmentation, deafness, and different colored irises. Even more promising, different people with Waardenburg syndrome express different combinations of these traits. One person might have a white forelock, one blue eye, and one brown eye, while a different person might have widely spaced eyes and deafness.

Waardenburg Syndrome

Waardenburg syndrome is an example of variable expression, which means that the same genotype can cause different phenotypes in different people. Variable expression is surprisingly common, even though scientists don’t have a great understanding of what causes it. Variable expression could be influenced by random chance, by environmental factors, by interactions with other genes, or by all of the above.

If Marvel ever decides to introduce a team of mutant superheroes whose powers include patchy skin coloration and widely spaced eyes, they will be on solid scientific ground. With the X-Men though, not so much.

First, there’s probably a limit on just how variable variable expression can be. “Different levels of expression can cause different phenotypes but it’s a little hard to come up with how that could be shooting lasers out of your eyes vs. predicting the weather,” said Dr. Ann Rougvie, a professor of genetics, cell biology, and development.

Second, we start to run into the same problem that we did before: it’s a lot easier to make things go wrong in a big way than it is to make things go right in a big way. Most mutations that cause multiple phenotypic effects do so because they knock out a gene that is important in several different developmental pathways. Mutations in genes that are more central in development will generally have more and bigger consequences.

Unfortunately, because what these mutations are essentially doing is playing havoc with an extremely important and fine-tuned process, those consequences probably won’t be good. If a mutation occurs in a very important gene, the most likely result is death before or soon after birth. Death is a pretty big effect, but not exactly the kind that we want.

So is the idea of real-life X-men dead? Probably. Sure, there is still a lot that we don’t understand about genetics and variable expression, and yes scientists have been wrong before. But from what we know today, which is actually quite a lot, the idea of X-men seems pretty far-fetched.

The final nail in the coffin? As Dr. Oetting explained, “Over the entire history of man, every nucleotide, every DNA base has been mutated. So if there was a mutation out there that resulted in people being turned into X-men, we would have run into it and it hasn’t happened.”

Thank you to Dr. Robert Brooker, Dr. William Oetting, and Dr. Ann Rougvie for their help in answering this question.

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* “Normal” is usually not a very accurate term to use when discussing genetics. Most genes have at least several alleles that are relatively common in the general population, so geneticists usually use the term “wild type” for the most common one.

**There are inheritance patterns that do not fall neatly into the standard dominant and recessive categories. For this reason and others, most geneticists look at several more factors than I did when using a pedigree to determine an inheritance pattern. I didn’t because it’s beyond the scope of this column and because I’m not actually getting paid for this.

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