“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?
In: 16
There is no such thing as a dominant blond gene, at least not in humans. Blond hair is always recessive trait, whether in Sweden or Algeria.
Thing is, though, recessive genes don’t simply disappear forever. If genetics worked that way, recessive genetic disorders like Tay-Sachs and cystic fibrosis would have disappeared long ago.
In terms of hair colors, it’s possible for a brunette and a blond to have a blond child if the brunette parent happens to have blond genes, which they might have as a result of having a blond ancestor at some point.
It’s also possible for two people with black or brown hair to have a blond child if they both happen to have the recessive blond genes. I believe the odds of this happening are about 25%, which isn’t high, but it’s still a long way from never.
I don’t know anything about hair genes but….
if blond is simple recessive it means lots of people with brown hair have some blond genes.
Recessive means the brown wins, the hair is brown and nobody knows the blond genes are hidden in them.
Two of those brown with blond genes people will have about 1/4 blond children.
Hair color in humans is probably more complex but this is the ELI5 version.
There is no such thing as a dominant blond gene, at least not in humans. Blond hair is always recessive trait, whether in Sweden or Algeria.
Thing is, though, recessive genes don’t simply disappear forever. If genetics worked that way, recessive genetic disorders like Tay-Sachs and cystic fibrosis would have disappeared long ago.
In terms of hair colors, it’s possible for a brunette and a blond to have a blond child if the brunette parent happens to have blond genes, which they might have as a result of having a blond ancestor at some point.
It’s also possible for two people with black or brown hair to have a blond child if they both happen to have the recessive blond genes. I believe the odds of this happening are about 25%, which isn’t high, but it’s still a long way from never.
I don’t know anything about hair genes but….
if blond is simple recessive it means lots of people with brown hair have some blond genes.
Recessive means the brown wins, the hair is brown and nobody knows the blond genes are hidden in them.
Two of those brown with blond genes people will have about 1/4 blond children.
Hair color in humans is probably more complex but this is the ELI5 version.
I don’t know anything about hair genes but….
if blond is simple recessive it means lots of people with brown hair have some blond genes.
Recessive means the brown wins, the hair is brown and nobody knows the blond genes are hidden in them.
Two of those brown with blond genes people will have about 1/4 blond children.
Hair color in humans is probably more complex but this is the ELI5 version.
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.
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.
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.
Say B is dominant brunette, and b is recessive blonde. If we start with a population that is 50-50 BB and bb, so half the population is brunette and half is blonde. Everyone couples up with the opposite color and we now have the next generation being 100% Bb, so everyone is brunette. The generation after that will be 25% BB, 25% bb, and 50% Bb. We now have 75% brunettes and 25% blondes. Even though blondes were “extinct” for a generation, they came back because their genes were always alive. If we look at the gene distribution: 25% BB, 25% bb, and 50% Bb. We see that it’s still 50-50 B and b just as the original population. The only way blondes get extinct is if they are seen as unfavorable, and don’t get as many partners.
Say B is dominant brunette, and b is recessive blonde. If we start with a population that is 50-50 BB and bb, so half the population is brunette and half is blonde. Everyone couples up with the opposite color and we now have the next generation being 100% Bb, so everyone is brunette. The generation after that will be 25% BB, 25% bb, and 50% Bb. We now have 75% brunettes and 25% blondes. Even though blondes were “extinct” for a generation, they came back because their genes were always alive. If we look at the gene distribution: 25% BB, 25% bb, and 50% Bb. We see that it’s still 50-50 B and b just as the original population. The only way blondes get extinct is if they are seen as unfavorable, and don’t get as many partners.
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