Two blue eyed parents can have a brown eyed child: How Nathan Petrelli can be born without abilities

Note: this was originally posted on my blog on I have tried to convert some of the formatting over, however there may be some inconsistencies. Also this particular entry was written before I knew how to cite scientific sources, so sources will either be nonexistent or incorrectly cited. 

This is an essay examining how a character with two parents with “powers” could be normal from a genetic point of view. I’ll specifically be looking at Nathan Petrelli from Heroes but it could be applied to Avatar the Last Airbender or Harry Potter with some modifications.

Disclaimer: I’m a biology student but it’s been a year since I took genetics and I don’t know everything. Feel free to point out anything that I got wrong.

Basic things to know about Nathan: In the show Nathan can fly, but it is revealed in the third season that these abilities were given to him as a child and that he was born without the proper gene to have an ability. (If it’s possible to genetically engineer someone after they’re a fetus is a different story that would get very confusing very quickly so I’m just going to assume that this is possible.) Everyone else in Nathan’s family has an ability naturally, including his brother Peter, you’ll see why this is important later.

Okay so for the actual science, I’m basing all of this off human albinism which if you’re interested you can read about here. There are also some basic words you need to know. An Allele is an alternative form of a gene that is located on a specific portion of a chromosome, there are two of these for each gene. ADominant Allele is the allele that will be expressed whenever it is present, not matter what other allele is, it will be represented by a capital letter like “A”. ARecessive Allele is an allele that is only expressed if there are no dominant alleles present, it will be represented by a lower case letter like “a”. Finally an individual is a Heterozygote when they have one dominant allele and one recessive allele, the organism will show the dominant allele, like “Aa”.

Albinism can be expressed in humans in many different ways. The physical traits of albinism are all fairly similar: pale skin, light hair, and light eyes that often result in vision problems. However a single mutation on one of many genes could cause all of these traits.

So let’s say you have gene A and gene B, both of which control cause albinism. An albino woman named Angela has a mutation on gene A and is albino, her code is aa. An albino man named Arthur has a mutation on gene B and is albino, his code is bb. Angela and Arthur have a child, this child is normal. But wait how can that be right?

This is because both Angela and Arthur have the mutation for albinism on two separate genes. So while their offspring will receive a mutant allele for gene A and gene B, the second allele will most likely be a normal allele. Therefore any offspring that Angela and Arthur have will be heterozygote for albinism on genes A and B, meaning that they will appear perfectly normal.

aa BB + AA bb = Aa Bb

When applied to Heroes this would mean that there are at least two genes that can give someone an ability (in the show it sounds like it is a single gene but I seriously doubt this due to the diversity of the abilities so let’s just assume that this isn’t the case or that they were talking about a genetic marker which is different). So to have an ability you have to have two mutant alleles in either gene A or gene B. Being heterozygote isn’t going to get you anything, you’ll just be fantastically normal. Congratulations.

Like in the albinism example Angela Petrelli has a mutation on gene A and can see the future, Arthur Petrelli has a mutation on gene B and can do…whatever exactly he does. They then have Nathan, who inherits a single mutant allele for gene A and gene B and a single normal allele for genes A and B, making him normal.

Okay that makes sense? But then how can Peter have an ability without the magic of genetic engineering? To fix this problem one or both of the parents would have to be a heterozygote. Let’s just assume it’s Angela. She has aa on gene A which gives her an ability, but she has bB on gene B. Due to random chance Nathan inherits an Aa Bb code while Peter inherits an Aa bb code, giving him an ability.

Nathan: aa Bb + AA bb = Aa Bb is normal

Peter: aaBb + AA bb = Aa bb has an ability

So that is how two parents with abilities can have a normal child. But how did Nathan retain his abilities? Why didn’t they malfunction sometimes like Traci or have horrible side effects like Mohinder? This is most likely because he had the genetic framework set up to have an ability.

So once again looking at genes A and B. Genes A and B would operate as two switches, producing some protein (which is what genes produce) that would allow other genes to be turned on to make the person have that ability.  So a person can fly? Well they better make the proper proteins that allow them to somehow defy gravity (anti-gravityase?). Nathan most likely inherited all these other genes, to make the proper proteins so he could fly, however he did not inherit an active gene A or B. The serum that he was injected with as a child somehow changed genes A and B so that one of them was aa or bb instead of Aa and Bb. Everything else was already in place. On the other hand Traci and Mohinder probably did not have a complete sequence of all the proteins that they needed for their abilities, so while their powers were switched on they did not function correctly one hundred percent of the time

#this makes a bunch more sense than my attempt  #which is the result of a liberal arts student muddling through wikipedia and half-remembered bio classes  #but there’s still the diversity of powers and the lines vs. random powers that get inherited to consider  #quietly hopes for more science-y meta by people who know more about science  (via tersyne)

Thanks! I’d love to read yours, just because I like to read about things like that. I can’t imagine trying to find information about genetics on wikipedia. I use it to study sometimes and it gets way too deep even for me.

For the lines (heredity) vs. random powers issue I actually have a theory on that. I’m going to put a “read more” because this got longer than I meant for it to be.

So there’s a subset of genetics called Epigenetics (a really good video about ithere.) Literally it’s “above genetics”. Epigenetics controls what genes are expressed and how much they are expressed. There are methyl groups that work like “switches” that turn genes on and off (a gene that is off does not produce a protein and do that thing that gene needs to do). There are also histones that coil and uncoil the DNA like yoyo’s that regulate how much that gene is expressed. So a gene could be turned on, but it’s really snuggly with the histone so not very much protein is made.

But really the most important thing about this is that epigenetics is affected by the environment that you live in as well as the genetic markers that you recieve from your parents.

So my theory is that a person’s ability manifests under a period of stress, this causes the genes that express their ability to be turned on, which explains why most people do not have their abilities from birth. Then once the ability is turned on depending on the stress that they are experiencing, their environment, the way that they grew up, how they are feeling, all affect what sort of ability is manifested.

You’re about to crash into the barrels on a free way? Well you better get out of there anyway you can. Is someone threatening to reveal information about you to the news papers? You better have a way to deal with that.

But this still is hereditary. You can inherit epigenetics from your parents as well as your own genes adapting to the environment around you. So Matt’s Dad was able to read minds, Matt was also able to read minds because by random chance he inherited his father’s epigenetic tag on those genes.


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