“The disappearing blonde gene was a hoax claiming a scientific study had estimated that natural blonds would become extinct, repeated as fact in reputable media such as the BBC and *The Sunday Times* between 2002 and 2006.”
“The hoax claimed that, because the allele for the genes for hair colour is recessive, blond hair would become less common as people with dominant non-blond hair alleles had offspring with people with the recessive alleles, even though such a pairing would retain one copy of the blond allele in the genome of the offspring. Claims that blond hair would disappear have been made since 1865.”
I’m trying to understand *why* it’s a hoax *and* how *the reality* works. To a layman and uneducated non-expert on genes, like myself, the premise of the hoax may at least *seem* logical:
If more and more people with the **dominant blond-hair gene** have offspring with people that have a **dominant non-blond gene**, then, eventually, the blond-hair gene may still *exist* but blond-haired people will be a rarity, because the blond-hair gene will be dominated by dominant non-blond genes. I mean, wouldn’t a traditional blond-haired, blue-eyed Swede only be born through two people with the dominant blond-gene?
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In high school biology, you were taught genetics through the example of Mendel and his pea plants. You are taught that genes have dominant and recessive, and by drawing a little Punnett Square, you can predict what percentage of offspring will have which trait.
None of this is untrue. The problem is, it only works for extremely simple genes.
It turns out that most physical traits in a human are not linked to single genes the way that, say, one of Mendel’s pea plant colors are. There is no single gene for “blonde“ to be dominant or recessive in the first place.
For example, eye color is linked to something like 16 different genes. There is no single dominant/recessive gene linked to “blue” or “brown” or “green.” It’s a combination about how all of those genes interact with each other. And sometimes, a completely unrelated set of genes like skin color will come along later and stomp the genes that otherwise would be setting you up for blue eyes in the first place. This happens a lot with babies.
Similarly, you will note that there are far more blonde young boys in the world than blonde fully-grown men. That is because testosterone has the effect of darkening hair color after puberty. It is also why body hair tends to be a darker shade than head hair. If you have genes that exaggerate this effect, then it doesn’t actually matter that your hair genes technically say you should be blond.
As a flip example, say that your hair genes say you should be brown-haired. But it turns out some other genes responsible for instructing the melanocytes in your hair follicles to actually make the hair brown are not functioning correctly. Ta dah, blond, even if you shouldn’t be.
It’s way more complicated than the simple four-quadrant Punnett Square you were taught in school. And that’s why it’s very unlikely that actual blonde people will disappear.
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