Fun fact, most people in the world are trichromats, they have 3 types of colour sensors in their eyes. One type of colourblindness that only affects men is where they only have 2 types of sensor and are dichromats - the gene is only found in the X chromosome, and it’s impossible for women with two X chromosomes to get the deficiency. However, it’s possible for women to get super genes and have 4 types of sensor, making them quadchromats. These ladies can see colours in between two other colours, that no one else can see. However, because the world is built by and for trichromats, this gift goes by largely unknown even by the people who have it.
This is not true. That women cannot have the congenital dichromacy (or anomalous trichromacy) that biological males commonly have is flat out wrong. A biological female can still be a protan or deutan, but the phenotype requires that both X chromosomes carry the recessive color vision-deficient alleles. Nevertheless, given that ~8% of all X chromosomes have such a gene regardless of sex, the incidence in the female population is still around half a percent, which is not insignificant.
Interestingly, one form of tetrachromacy in females actually has the same cause as color vision deficiency in some males (specifically anomalous trichromacy). From what I understand, only one X chromosome is active per cone cell, and which one is active is random. So, half of such a person’s cone cells of one type are “normal” while the rest of that type are anomalous and have a slightly different peak wavelength. The net result is four different types of cone cells, i.e., tetrachromacy, which may have an incidence of more than 10% in females.
X-inactivation is a little bit more complicated than that. While the process of X-inactivation initiation is random, once a cell has settled on one chromosome, all its daughter cells will silence the same chromosome. The initial process happens in the early embryo, so large patches of the body have the same X chromosome silenced.
This pattern is visible in some animals. E.g. a tortoise cat’s pattern arises due to the hair color gene existing on the X chromosome. Consequently, male tortoise cats are rare (XXY, XXXY etc only)
Neat, thanks for the clarification. Even though the initial proportion is 50/50 for X-activation, are there scenarios where one daughter line is more prominent than the other, or does it usually remain 50/50?
Statistics would indicate that that is a plausible scenario.
In addition, a uniparental disomy can occur as well. Here, the X chromosome was duplicated in the egg cell. So the exact same X chromosome is inherited twice.This is an error in meiosis. This could occur in XXX (with the third X from the father’s side), XXY, or even XX. That latter one would be rare, for a uniparental disomy on X without a third sex chromosome would mean both egg and sperm cell had an error during meiosis.
You could also see a single X (Turner Syndrome) as a 100% dominant X-chromosome. But that may be semantics.
the gene for red green color blindness is carried on the X chromosome so a woman can have it it is just very rare. Now blue yellow color blindness is much much rarer and carried on a different chromosome so men and women have it equally
Fun fact, most people in the world are trichromats, they have 3 types of colour sensors in their eyes. One type of colourblindness that only affects men is where they only have 2 types of sensor and are dichromats - the gene is only found in the X chromosome, and it’s impossible for women with two X chromosomes to get the deficiency. However, it’s possible for women to get super genes and have 4 types of sensor, making them quadchromats. These ladies can see colours in between two other colours, that no one else can see. However, because the world is built by and for trichromats, this gift goes by largely unknown even by the people who have it.
It is possible for women to be colorblind (if their father is colorblind and their mother is a carrier for the gene).
It is also possible for men to be tetrachromats if they have XXY genes (called Klinefelter syndrome).
This is not true. That women cannot have the congenital dichromacy (or anomalous trichromacy) that biological males commonly have is flat out wrong. A biological female can still be a protan or deutan, but the phenotype requires that both X chromosomes carry the recessive color vision-deficient alleles. Nevertheless, given that ~8% of all X chromosomes have such a gene regardless of sex, the incidence in the female population is still around half a percent, which is not insignificant.
Interestingly, one form of tetrachromacy in females actually has the same cause as color vision deficiency in some males (specifically anomalous trichromacy). From what I understand, only one X chromosome is active per cone cell, and which one is active is random. So, half of such a person’s cone cells of one type are “normal” while the rest of that type are anomalous and have a slightly different peak wavelength. The net result is four different types of cone cells, i.e., tetrachromacy, which may have an incidence of more than 10% in females.
X-inactivation is a little bit more complicated than that. While the process of X-inactivation initiation is random, once a cell has settled on one chromosome, all its daughter cells will silence the same chromosome. The initial process happens in the early embryo, so large patches of the body have the same X chromosome silenced.
This pattern is visible in some animals. E.g. a tortoise cat’s pattern arises due to the hair color gene existing on the X chromosome. Consequently, male tortoise cats are rare (XXY, XXXY etc only)
Neat, thanks for the clarification. Even though the initial proportion is 50/50 for X-activation, are there scenarios where one daughter line is more prominent than the other, or does it usually remain 50/50?
Statistics would indicate that that is a plausible scenario.
In addition, a uniparental disomy can occur as well. Here, the X chromosome was duplicated in the egg cell. So the exact same X chromosome is inherited twice.This is an error in meiosis. This could occur in XXX (with the third X from the father’s side), XXY, or even XX. That latter one would be rare, for a uniparental disomy on X without a third sex chromosome would mean both egg and sperm cell had an error during meiosis.
You could also see a single X (Turner Syndrome) as a 100% dominant X-chromosome. But that may be semantics.
It’s not actually called quadchromatism but tetrachromatism.
I once knew a girl who was colorblind. Both her parents were too. It’s rare but it can happen.
How the mom got colorblind?
Food poisoning
the gene for red green color blindness is carried on the X chromosome so a woman can have it it is just very rare. Now blue yellow color blindness is much much rarer and carried on a different chromosome so men and women have it equally
I didn’t know her well enough to ask. She was a friend of a friend, and this was over a decade and a half ago.
My daughter has the super eyes. She looooves pointing out different colors that “daddy can’t see!” Lol.
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I’m a male designer, and have a good eye for color. Am I a mutuant?
No, you just think you’re good. 😊
Thanks for posting this, had no idea!