Ever wonder where red hair comes from? I don’t mean how it originated. For that, we have the Legend. I mean how it is passed from parents to their children, especially from parents who appear not to have it.
Unfortunately, in this area, myths abound. In Red Prince’ Genetics Lab we shall attempt to separate fact from fiction.
Generally, red hair, just as any other biological trait, is transferred from parents to children through genes. I said generally, because there is such a thing as genetic mutation, so it is conceivable one could “develop” red hair without receiving it from his parents, and then transmit it to his children. Or, for that matter, one could develop the red gene without it having any effect on his own hair color, but transfer it to his children who then may be redheads. Conversely, one could lose it. These would be exceptions to the rule, but, as I said, they are conceivable.
Genetics for Geeks
I do not claim to be an expert on genetics. But I have been fascinated by the subject since the sixties when I spent two years in medical school. No doubt, many new facts and insights have come to light since then, but I do believe I have a decent understanding of the very basic principles of the transmission of genetic traits. I will attempt to express these principles in the language easy to understand by “geeks” (hey, this is the Internet!). I also have several links to genetics web sites for the rest of us in Red Prince’ Global Chamber.
First off, traits are expressed in the form of “genotype”, which in geek-speak is nothing but a binary lookup table.
As in any binary code, each gene can be on or off, true or false, one or zero. That is, one gene defines that your eyes are either big or small, another one that your cheeks are freckled or not freckled, etc.
Some traits use more that one gene, or one bit in the lookup table. Otherwise, everyone’s hair, for example, would be either fair or dark. We know that is not the case: There is a whole scale of hair colors. Incidentally, these traits are called “polygenic”. Please remember that word, as I will mention it when discussing the genetics of the skin and hair color.
Of course, we inherit our genetic traits from both our fathers and our mothers, and both parents do not necessarily pass the same binary data to us. As it happens, we inherit two lookup tables, one from father, one from mother. Each gene then comes in pairs, or alleles, as geneticists call them.
Since the two bits are not necessarily the same, one usually “wins.” In the language of genetics, one is dominant, the other recessive. If both bits say the same, of course, that is the trait we have inherited. If not, the dominant wins. But in that case we still pass the recessive one to 50% of our children. That is why, for example, two brown-eyed parents can have a blue-eyed child, but two blue eyes cannot conceive a brown eye (well, except, perhaps, if a mutation happens, but a blue-eyed mother would probably have hard time convincing a court that a blue-eyed man is the father of her brown-eyed child).
Translated to geek-talk, the dominant bit is boolean one, the recessive is boolean zero. They are logically ored to determine which trait we have inherited.
Well, I did say usually, didn’t I. That’s because some genes are actually ternary, not binary. The bits from the allele—the corresponding bits from both lookup tables—are arithmetically added, which gives us three possibilities: 0, 1, or 2. In other words, we either don’t have the trait at all, or have some of it, or have all of it. You may see it referred to as “incomplete dominance”, or by other names. Remember this, it will be important later when we get to the genetics of red hair!
Furthermore, all bits of polygenic traits—from both tables—are also added up, but for more than three possibilities.
You are probably aware that in centuries past most people were much shorter than we are today. Does that mean human genes have gradually gone through a series of mutations which resulted in taller people?
No. Genes have not changed. Our environment did. We eat healthier food than our ancestors, so our bodies have received better nutrients during our growing years. This brings us to the concept of “phenotype.” While the genotype is the lookup table which lists what traits we are supposed to have under ideal conditions, there may be factors that either interfere with the biochemical process of translating the genetic code to biological phenomena, or at least influence it in some different way. The result of this translation, the actual biological traits we develop, is called phenotype.
I am not going to discuss the process of the translation of genotype into phenotype here. Not that it is not interesting, but it would take us to details not necessary for the study of how red hair is inherited. If you want to learn more, visit the genetics links from my Global Chamber.
Nor am I going to spend much time on mutations. Let me just say that, unlike in a computer, the genetic lookup table is not written into silicone. It is encoded into complex molecular structures. Each structure encodes both the bit value of the gene and its position within the table (that is, which gene this molecule represents).
Of course, chemical structures can be changed by the presence of other chemicals, by physical surroundings (e.g. radiation), even by the state of mind. For that matter, chemical changes can be affected by societal happenings. How else can we explain the fact that shortly after World War II in which many men died considerably more boys were born than girls. This is perfectly understandable: Societal happenings influence the state of mind of its members, while the state of mind influences the chemistry of its biological organism.
All these influences can cause mutations, for better (e.g. adaptation) or worse (e.g. skin cancer).
Genetics and Erythrology
What the heck is “erythrology”? Well, I just needed to name this topic something, so I made up that word. It’s Greek for “red science,” a perfectly good name for the study of red hair. I guess I could have called it “erythrocephalology,” that is, “red head science,” but who needs big words like that?
Anyway, before we can talk about red, we need to take a look at brown. It will soon become clear why. Until then, please, bear with me.
A protein called melanin is the brown pigment present in human skin and hair. The less melanin, the fairer the skin and hair. The more melanin, the darker the skin and the hair become. Melanin, by the way, protects the skin from harmful UV rays.
Skin color is polygenic. You will recall that means it is genetically determined by several gene sets (alleles). Specifically, there are three of them. Since each allele contains two bits (gene values), that combines to six bits altogether.
Remember that in polygenic traits the bits are added up, not ored. With six such bits there are seven possible results: Zero when all bits are recessive (0), six when they are all dominant (1). And there are, of course, seven values in a set from zero through six. The lesser the result of polygenic addition, the less melanin, hence, the fairer the skin. The greater the result, the more melanin, hence, the darker the skin.
Hair color, too, is polygenic. I am not yet talking about red hair here.
Hair color is determined by four gene sets. With two alleles per set, it gives us eight possible bits. They can add up to any value from zero to eight, for a total of nine hair colors.
Again, the lesser the value, the less melanin, hence, the fairer the hair. The greater the value, the more melanin, hence, the darker the hair.
Now you may be thinking, wait a minute, there are more than nine shades of hair color between totally blond and black. That’s true. But genotypically, there are only nine. Phenotypically, there can be any number, since phenotype is influenced by other factors than genotype alone.
Note that hair color and skin color are determined independent of each other. You can have pale skin and black hair. And, theoretically, you could have black skin and blond hair. That the latter case is rare, or perhaps even non-existent, is caused by the fact that people living closer to equator need more protection from harmful UV rays, so they developed both dark skin and dark hair. This took a long time to develop. But, as nowadays people have moved, or been forced to move, to different parts of the world, it is quite possible that more and more people with dark skin and light hair will be born.
Two genes are responsible for freckles. But they are not polygenic. Rather, one determines whether you have freckles on your cheeks, the other, on your forehead.
They follow the usual dominant/recessive model, so if you have at least one dominant bit (binary 1), you will have freckles. If both bits (genes in the allele) are recessive, no freckles.
Of course, this is determined separately for cheeks and forehead.
Ah, finally we have arrived! I saved the best for the last.
So, how many gene pairs control the red haircolor?
Surprise, just one. With incomplete dominance. That means your hair is either not red at all, or medium red, or very red. That's it! Only three possibilities!
Now, that does not sound right, does it. There is strawberry blond, there is light red, bright red, flame red, there is light auburn, dark auburn, cinnaberry (oops, that’s a hair dye, nothing to do with genetics). Something does not add up.
But that’s just it! It “adds up.” The red blends with the brown for a large number of combinations.
In fact, since there are two levels of red and only one of not red, there are twice as many possible blends of red and brown than all the shades of blond and brunet combined.
For the world’s smallest minority, redheads sure come in large variety! Hear that! Consider the obvious consequence:
By their very nature, redheads are more original than all blonds and brunets combined!!!
The blending of the red and brown hues may also render the red color invisible. People who have only one red gene and very dark hair may never know that they, in reality, are redheads!
If a red-haired child is born to two parents with brown hair, it is not because the red gene is recessive, as is commonly believed. Rather, it is because at least one of the parents is a redhead in disguise. Maybe even both!
If you have both red genes, and otherwise blond hair, your hair will probably be of flaming red color. If you have only one red gene, and blond hair, you will probably have strawberry blond, or perhaps light red hair. If you have both red genes and lots of brown, you may have dark red or auburn hair. And so on, you can do the math yourself.
Incidentally, there is a common belief that if both parents have red hair, all their children will be redheads. This is based on the same misconception that red hair is caused by a recessive gene.
However, as we have discovered, it is possible that both redheaded parents have only one red gene. In that case, one quarter of their children will inherit the red gene from both parents, one half from one parent only. And the remaining quarter will not inherit even one red gene.
Test Your Understanding
Finally, a little quiz for you. Just two questions. If you answer both correctly, give yourself the degree of Master of Science in Erythrology or MSE.
Here’s what actor Noah Hathaway looks like, or at least did look like, back in 1984. Brown hair, no freckles.
Suppose we could somehow genetically “re-engineer” him and implant him with genes of our choice.
All else being the same, if he had two red genes, i.e., the red gene in both alleles,
Once you have decided on your answer, please click on Noah’s picture to see the test results.
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