“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
Two parents, both with one brown hair gene (Br) and one blond hair gene (Bl).
They decide to have children, so each of their children inherits ONE hair color gene from each parent, selected at random by the cellular process that produces eggs and sperm.
Some of their children will end up inheriting one Br from each parent and no Bl, some will inherit one Br and one Bl, and some will inherit one Bl from each parent and no Br.
The ones that get at least one Br will have brown hair, but the ones that don’t get any Br and only get Bl will have blonde hair.
So as long as the genes are present, the possibility of them being expressed continues to exist.
Two parents, both with one brown hair gene (Br) and one blond hair gene (Bl).
They decide to have children, so each of their children inherits ONE hair color gene from each parent, selected at random by the cellular process that produces eggs and sperm.
Some of their children will end up inheriting one Br from each parent and no Bl, some will inherit one Br and one Bl, and some will inherit one Bl from each parent and no Br.
The ones that get at least one Br will have brown hair, but the ones that don’t get any Br and only get Bl will have blonde hair.
So as long as the genes are present, the possibility of them being expressed continues to exist.
Two parents, both with one brown hair gene (Br) and one blond hair gene (Bl).
They decide to have children, so each of their children inherits ONE hair color gene from each parent, selected at random by the cellular process that produces eggs and sperm.
Some of their children will end up inheriting one Br from each parent and no Bl, some will inherit one Br and one Bl, and some will inherit one Bl from each parent and no Br.
The ones that get at least one Br will have brown hair, but the ones that don’t get any Br and only get Bl will have blonde hair.
So as long as the genes are present, the possibility of them being expressed continues to exist.
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.
Dominant genes don’t always stop recessive genes from being passed on and therefore expressed. If you look at a [punnett square](https://image.slidesharecdn.com/gregor-mendel-punnett-squares-119723542281563-4/95/gregor-mendel-punnett-squares-22-728.jpg?cb=1197206623) of brown and blond hair as an example, it makes it a little more obvious.
While the blond gene has a 25% chance of being expressed, it has a 75% chance of being passed on. If that child then has a child with someone else who has a recessive blond gene, no matter if both parents are brunet, the gene can still be passed on and even expressed.
Dominant genes don’t always stop recessive genes from being passed on and therefore expressed. If you look at a [punnett square](https://image.slidesharecdn.com/gregor-mendel-punnett-squares-119723542281563-4/95/gregor-mendel-punnett-squares-22-728.jpg?cb=1197206623) of brown and blond hair as an example, it makes it a little more obvious.
While the blond gene has a 25% chance of being expressed, it has a 75% chance of being passed on. If that child then has a child with someone else who has a recessive blond gene, no matter if both parents are brunet, the gene can still be passed on and even expressed.
Dominant genes don’t always stop recessive genes from being passed on and therefore expressed. If you look at a [punnett square](https://image.slidesharecdn.com/gregor-mendel-punnett-squares-119723542281563-4/95/gregor-mendel-punnett-squares-22-728.jpg?cb=1197206623) of brown and blond hair as an example, it makes it a little more obvious.
While the blond gene has a 25% chance of being expressed, it has a 75% chance of being passed on. If that child then has a child with someone else who has a recessive blond gene, no matter if both parents are brunet, the gene can still be passed on and even expressed.
Same as with red hair being able to pass through generations and two browned eyed people having blue eyed kids
Brown hair (BB) and blonde hair have a kid(bb)
The kid has (Bb) brown hair*
The kid grows up has a child with another brunette(Bb)
Their child has the chance to be blonde (bb)
If the original kid of the first two parents has a child with a blonde(bb) than their child has equal chances of having blonde(bb) or a brunette hair
* way way more than a single gene is related to hair color. And way more than allele probability affects phenotypes, including mutations, hormonal changes(if your hair got darker/straighter/curlier as you got older this is why) and the tightness of the curl of DNA and more!
Same as with red hair being able to pass through generations and two browned eyed people having blue eyed kids
Brown hair (BB) and blonde hair have a kid(bb)
The kid has (Bb) brown hair*
The kid grows up has a child with another brunette(Bb)
Their child has the chance to be blonde (bb)
If the original kid of the first two parents has a child with a blonde(bb) than their child has equal chances of having blonde(bb) or a brunette hair
* way way more than a single gene is related to hair color. And way more than allele probability affects phenotypes, including mutations, hormonal changes(if your hair got darker/straighter/curlier as you got older this is why) and the tightness of the curl of DNA and more!
Same as with red hair being able to pass through generations and two browned eyed people having blue eyed kids
Brown hair (BB) and blonde hair have a kid(bb)
The kid has (Bb) brown hair*
The kid grows up has a child with another brunette(Bb)
Their child has the chance to be blonde (bb)
If the original kid of the first two parents has a child with a blonde(bb) than their child has equal chances of having blonde(bb) or a brunette hair
* way way more than a single gene is related to hair color. And way more than allele probability affects phenotypes, including mutations, hormonal changes(if your hair got darker/straighter/curlier as you got older this is why) and the tightness of the curl of DNA and more!
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