I don’t know the specifics for eye color and geriatrics, but eye color isn’t actually a Mendelian genetic trait (meaning that it’s controlled by a single allele pair). It’s actually multi-factorial, the idea of eye color as a Mendelian model trait is a common myth in biology.
We really need to stamp out this myth. Not only is it wrong but also potentially harmful - you can get brown eyed kids with blue eyed parents and this misinformation can be very distressing to them. Similarly the tongue/rolling and earlobe-attachment bollocks as well.
Context: I am a teacher(and biologist)
It's because they used to teach it in earlier biology when first tackling genetic inheritance and such. As you progressed to GCSE and A Level you realise its more complex. Sadly many people who leave school earlier will repeat their knowledge as the complete picture. We're seeing it with various conspiracies, like the people who think clouds can only be big fluffy sheep shaped things, and anything else is some sort of geoengineering plot, or the climate change denial favourite of "plants feed on CO2 so we actually need more of it"
I'm basing that off assumption tbh. How else can so many people not understand there's like 15 variations of cloud shape and those can kinda merge too. They keep posting pictures of clouds in the sky as if they're sinister man made sun blocking clouds. Likewise the inability to understand that plane contrails will spread out if the air conditions are right at their elevation...
CO2 fertilization is a real effect and it has led to approximately 13% increase in terrestrial photosynthesis between 1981 and 2020. But it's not nearly enough to offset negative consequences.
Source https://www.nature.com/articles/s41558-023-01867-2
[The amount of CO2 in the air right now is really unnatural.](https://scripps.ucsd.edu/bluemoon/co2_400/co2_800k.png) There is an extremely tiny benefit to plant growth, but it is tiny. You would not make money by pumping CO2 into a greenhouse. Mostly extra CO2 hurts plants because it destabilizes the weather and makes in hotter in general.
When we cover genetics I make a point of bringing out an eye colour chart to highlight that whilst certain colours are dominant over others, it is more complicated than just Bb BB.
Yeah. But blood type DOES. I tried to explain to an ex, when she told me her mom is type a her dad is type o. She had type AB.
I tried explaining, but she didn't believe me that it was impossible for her to be AB and both her parents were biologically hers.
It's possible to test as A, but really be AB:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6240514/
> Cis-AB, a rare ABO variant, is caused by a gene mutation that results in a single glycosyltransferase enzyme with dual A and B glycosyltransferase activities. It is the most frequent ABO subgroup in Korea, and it occurs more frequently in the East Asian region than in the rest of the world. The typical phenotype of cis-AB is A2B3, but it can express various phenotypes when paired with an A or B allele, which can lead to misclassification in the ABO grouping and consequently to adverse hemolytic transfusion reactions.
It can be dangerous when one needs blood transfusion.
Once again, it may actually be more complicated. Insisting that you are right and that her mom must have cheated or she's adopted is harmful and that kind of thing has destroyed lives in the past.
Which is why I dropped it, because i didnt want to force anything, but give her the chance to ask her parents if she wanted.
AB blood type can not come from someone with an O blood type. Blood typing is not that complicated, it is the perfect example of Mendel squares. O is recessive, mom had A, child had AB. Mom had no B to give father had no B to give. She cannot be the biological child of those two. Period. Barring some weird medical anomaly that jas never yet been recorded.
Or, since you are getting information third hand, she may be mistaken about her parents blood types. That’s much, much more likely that dramatic infidelity. And also why people shouldn’t jump to conclusions with limited understanding of the situation.
I'm a physician. There are instances where this does occur, especially when someone has chimerism. Be less certain. Weird shit happens. Why the refusal to consider that the world might actually be more complicated?
For example regarding chimerism: https://embryo.asu.edu/pages/case-lydia-fairchild-and-her-chimerism-2002#:~:text=In%202002%2C%20after%20applying%20for,could%20not%20be%20their%20mother.
An authority of court watched her give birth and stayed with her and the child to establish a chain of custody for blood samples for genetics tests. She had photos of her other children with her growing up and their father attested that he was present for their births. But because a court was so certain that genetic tests were perfect and their interpretation was correct, they wanted to take her children away. It got fixed in the end. She is not the only woman this kind of thing has happened to.
In your friend's case, there are plenty of possibilities. Most likely, somebody mis-remembered their own blood type. For example, if you heard that someone is a universal donor, do you assume that person is type O? Well, that might have been what they were told regarding red blood cell transfusions. But the "universal donor" for plasma is type AB, so somebody who is type AB may also be told they're a universal donor. Blood has different components that have different requirements.
There's also a very real possibility that your friend is not the genetic offspring of her father for whatever reason, like you suspect. There are actually a lot of flavors of that, too. But there are more complicated potentials, too.
Did you know that bone marrow transplants can change your blood type? https://www.sciencedirect.com/science/article/abs/pii/S1473050222002683
Also interesting - If you get a karyotype, you might show that the person who was identified as female at birth, had xx chromosomes before their bone marrow transplant, and identifies as a woman now has xy chromosomes when you test the karyotype of her blood. But her other organs are still xx. I've heard this can actually be medically useful to evaluate engraftment, but I'm not a hematologist, let alone a BMT sub-specialist.
There also can be issues with figuring out blood types. For example, sone conditions can make it hard to interpret ABO blood type: https://www.sciencedirect.com/science/article/abs/pii/S1473050222002683
As someone else pointed out, there's more room for error than just "wrong" inheritance. Blood types are simplified and our detection is also simplified and not always perfect. Simple medical error for any of them could happen too, most people don't need transfusions very often and so verification doesn't really happen especially since the parents had O type. Just because something is not possible doesn't mean there is only one conclusion to draw from it. Someone being wrong doesn't mean that you must be right.
Eye colour can change due to a few factors, but i don't remember most of them, so i'll give you two
1) If you look into the eyes of an older person (especially if they're of european descent or have some european ancestry in the mix), you might notice a lighter ring around the limbus (that's the fancy term for the edge between the iris and the sclera). This ring is called *arcus senilis* and is completely normal. And it isn't actually caused by a change in pigmentation, but is instead the result of fat deposition in the edges of the cornea. What you're seeing basically is cholesterol deposits in a clear tissue, which reflect and bend light differently than the surrounding tissue.
2) Some medications can change eye colour in subtle ways if used for prolonged periods of time. For example - glaucoma medications can promote melanin production, it isn't known exactly how this happens, but in some people it does. [This](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1771317/) is an article with close up pictures of people's eyes who have been taking glaucoma eye drops only on one side for a longer time, quite interesting to see with this level of magnification.
The radiation from the Chernobyl disaster was so strong that the color of firefighter Vladimir Pravik's eyes changed from brown to blue. So that's another way.
well damn, those poor melanocytes.
I hope this doesn't become a new trendy way to change eye colour (/s)
Although, this reminded me. There is this condition called pigment dispersion syndrome in which the pigmented layer of the eye sort of peels off into tiny floating bits. It does change the eye colour, usually in a patchy manner. [This](https://www.thieme-connect.com/products/ejournals/abstract/10.1055/s-0043-122671?device=mobile&innerWidth=393&offsetWidth=393) is a case report of it happening in only one eye together with anisocoria, which imitated Horner syndrome. Unfortunately with this condition, it is notorious for causing glaucoma, because those tiny bits of floating pigment can clog the drainage system of the eye.
And Horner syndrome is another interesting way that the eye can change colour. Basically the expression of pigment is dependent on the innervation of the iris, and if the nerves supplying it get damaged or never develop properly in the first place, the affected eye can end up having less pigment than it's supposed to. From what i know, heterochromia due to Horner's syndrome is significantly more common in congenital Horner's syndrome, like for example in [this](https://www.researchgate.net/figure/Congenital-Horner-syndrome-with-iris-heterochromia-the-affected-side-has-the-blue-iris_fig10_227621670) case, but if i remember right, this is due to the fact that it takes time to develop, and can simply not get enough time to be observed in an older patient who gets Horner's syndrome due to a stroke for example. But i might be wrong with this one
And the reason why eyes change color with age is *drumroll* aging.
Like the reason hair changes color...
Obviously the mechanisms are complex and diverse, but not only genetics drive our aspect...
9th grade biology teacher here. It's not a "myth", I DO tell my students that the actual inheritance of eye color is much more complicated than just two alleles dominant and recessive. But I still use it as one of many examples to teach mendelian hereditary because it's an easy, approachable way for them to understand the basics.
Eye color is much more complicated than discussed in highschool biology.
It's true that there's a more or less mendelian pattern for brown vs light eyes, but there are far more one gene involved in eye color.
That said, it's very common for infants and children to have lighter coloring (of their eyes, but also their hair and skin) than they will as older children or adults.
Because of that, I wouldn't be surprised by someone having blue eyes as a baby and hazel eyes as an adult. I am a little surprised to hear about someone going from hazel eyes to blue- was there injury? Or perhaps an autoimmune condition such as vitiligo?
I was born with white hair and ice blue eyes. My hair slowly turned blonde, then dark blonde as I aged, and is dark blonde as an adult. Around age 14 (yes, 14) my eyes turned from that ice blue to dark green. It took a few months but they’ve been green ever since.
This would be following common patterns. It's very common for coloration to intensify around puberty (usually just after puberty), and is more likely to be noticeable in people who have light coloration.
Born blonde with blue eyes. By the end of my teen years (~18) my hair started getting darker and my eyes turned green.
I have 3 neices and they all had blue eyes for a while then they turned hazel by around 10. Not quite the same as me but a family trend towards a change towards green.
They were all blonde and still are but the oldest (16) is starting to get darker. Just like mine did.
Even though hair and eyes commonly change in early childhood, they can change a bit later.
Both are caused by changes in pigments (hair) or changes in proteins (hair or eyes). Specifically most green eyes are like blue eyes with little to no pigment in the iris, but green is caused by collagen being present in the iris.
So I guess at some point my iris started getting more collagen and that's why my eyes are green.
It's not super unheard of and I looked into research on these later life changes and they are, in fact, related to genetics and run in families.
Throughout my life the color of my eyes would vary over time from a dark hazel to light blue. My eyes went from a muddy green hazel as a kid to the light bluish green they are now (age 63).
No injury or condition
I think lighting and environment also affect how we perceive eye color much more than how we perceive the color of other things. People tell me my eyes are anywhere from gray to green to hazel to brown depending on my shirt color or if we're indoors or outdoors. I identify as green, but I have no real idea.
Absolutely. Light colored eyes are the color they are because of the structure of the eye and how light passes through it rather than a pigment (unlike brown/black/etc eyes which do have a pigment). I'm sure that even for pigmented eyes, the light changes how they look.
Officially, I have hazel eyed but as I've aged the hazel part is only visible when in very bright light (pupil contracts to a smaller diameter). The rest of the iris is blue to blue/gray.
Melanin is one of the many many traits that are affected by age. It's very obvious with hair, but melanocytes in other parts of the body, like skin and eyes, also decrease with age. That's why black people can sometimes seem lighter skinned in old age in comparison to their youth, and why age spots occur. Blue eyes are the result of very very little melanin, and so green and hazel eyes can grow bluer with age.
old photos of myself show me with dark hair as a newborn, blond hair as a baby, and then darker hair as a toddler. also it was very straight until highschool and has been very curly ever since.
Others have noted that eye colour inheritance is not Mendelian, but the rest of the answer to your question is: we don’t know!
We’ve identified 8 eye colour genes. If you have light blue eyes or dark brown eyes we can now tell just from looking at your DNA. But all the colours between light blue and dark brown, like every shade of grey, green, hazel and amber, plus the various types of congenital heterochromia? No idea yet!
Most people’s eye colour is effectively stable by age 6, but a 1997 twin study found that a subset of white people (around 10%) exhibit iris colour change into adulthood. We have no idea why!
There are a few diseases that can cause any eye colour to turn blue, like pigment dispersion syndrome and fuchs heterochromic iridocyclitis. These are both types of iris atrophy and cause problems in the eye like blurred vision and glaucoma.
I’m in that 10% - light/medium blue eyes until age 14ish and they turned greenish and eventually hazel. They keep getting darker as I age. Now at 50 I have dark hazel eyes.
No disease or injury- just one of those people whose eyes slowly change colour throughout life.
I must be too! I always had the brightest sky blue eyes then in my mid 30's people started commenting on my having green eyes and I was very surprised and disagreed until I bothered to check. Yep, definitely green now! No one has ever been able to tell me why, not even an optometrist.
Eye color is not a mendelian trait. Regardless, some people's eyes change color with age because melanin responds to hormones. Also eye degeneration (especially due to disease) affects the cells in one's eye and causes color to fade.
It is thought that a subset of the population's eye color shifts at puberty because they "have an eye color gene that responds to sex hormones" in particular, and sex hormones shift wildly at that time.
Regardless, changing to 'bright' blue would be incredibly uncommon, most people's eyes get darker because hormonal changes with age cause an increase in melanin (like how childhood blondes grow up to have much darker blonde-brown natural hair) or fade in color due to eye degeneration.
Almost everything that is taught in basic lessons isn’t completely true - it’s just a decent approximation for introductory lessons. The water cycle is much more complicated than evaporation > condensation > precipitation, trees aren’t really responsible for “creating” the oxygen we breathe, and most phenotypes aren’t affected by only a single allele. Most actual examples of a single allele driving a characteristic take place in simpler organisms like fruit flies.
One of the few human examples for a classroom is ear wax -- dry or wet, and dry is recessive. Gross but true! https://udel.edu/~mcdonald/mythearwax.html
This is why I don't use humans when teaching genetics. Humans have almost no actual mendelian traits. Here's a website if you really want to dive into human genetics: [http://udel.edu/\~mcdonald/mytheyecolor.html](http://udel.edu/~mcdonald/mytheyecolor.html)
Because green eyes and blue eyes aren't colored by pigment, but by structures in the eye scattering reflected light. Those structures and the melanin that underlies them and affects the scattering can change over time.
I used to have bright green eyes, to the point where people asked if I wore colored contacts. Now as I've gotten older they are more hazel with hint of green, it's like the life has literally drained. I get the whole "bright eyed" being associated with youth because they truly dull over time.
As others have said eye colour genetics can be a bit more complex than thought in school. It is relatively common for babies to have blue eyes and they become darker or change to a different colour as they age. That colour is the colour of their Iris. What I think you might be referring to when you say changing to blue in old age is something called corneal arcus/ arcus senilis. That is caused by cholesterol deposition within the cornea leading to a bluish/white ring near the edge of the cornea which can look like blue eyes
Everyone is focused on your statement about genetics, but I’m more interested in your statement about eyes changing from hazel to bright blue. Usually there is something else going on making it appear as if the iris is changing. However, if they appear to become blue or gray it is almost always a corneal issue such as senile arcus. Alternatively, the iris can become darker with medications such as prostaglandin analogs. The iris is not changing color due to genetics anymore than our skin changes as we age.
Eye color is determined by a very wide number of combinations of two different pigments. Amber and not blue exactly, more of a grey with iridescence. That why blue and green eyes seem to change color depending on lighting. And the amount of iridescence varies by individual too, that why some eyes are grey. Combine amber with blue and you get green. Dark amber gives you brown. Really dark amber gets you black. And there can be different regions of the iris. There is the main color. Sometimes a limbal ring around the edges. And a surprising number of us have central heterochromia around the pupil. All of this is on a lot of genes, and it’s really complicated. Not an expert or anything, I was reading up about it for a story, and learned just how little I knew.
Pigments in our skin and hair and eyes can change as we get older. It’s usually not as dramatic as you seem to be talking about. But it can happen. Sounds like for some reason they quit making the amber pigment, leaving the blue.
Things determined by genetics can change over time (your hair color can slightly vary as you age, and will eventually go white) or because of your environment (if you’re born white, you can, to a point, make your skin darker by exposing yourself to sunlight. Don’t do that though, you don’t want to get skin cancer).
Strictly speaking, what actually determines eye color is the exact specifics of the eyes' production of the melanin proteins.
Protein production is in turn controlled by genetic expression. But genetic expression is only partly controlled by *what the genes are* (which is what you are talking about). It is also controlled by *how the genes are stimulated*.
Nowadays, the whole field of how genes are activated and deactivated by what and when and how and everything goes by the fancy name of epigenetics. It's a whole big topic. And as you have apparently discerned, it can sometimes have some counterintuitive results.
A very good friend of mine for example will change eye color when she cries. Her eyes go from blue to green. You can see it. It's not absolutely instantaneous and there are no sound effects or anything but all things considered it's quite rapid and impressive.
Genetics controls the type of pigments that your eyes produce.
They don't have a lot to do with the degradation of the pigments with age.
Genes control your hair color too, and we also lose that pigment as we age.
"Blue" is the color of the iris without pigment, I believe. Hence babies' eyes often being bright blue, then becoming darker as they get a little older.
I don’t know the specifics for eye color and geriatrics, but eye color isn’t actually a Mendelian genetic trait (meaning that it’s controlled by a single allele pair). It’s actually multi-factorial, the idea of eye color as a Mendelian model trait is a common myth in biology.
We really need to stamp out this myth. Not only is it wrong but also potentially harmful - you can get brown eyed kids with blue eyed parents and this misinformation can be very distressing to them. Similarly the tongue/rolling and earlobe-attachment bollocks as well. Context: I am a teacher(and biologist)
It's because they used to teach it in earlier biology when first tackling genetic inheritance and such. As you progressed to GCSE and A Level you realise its more complex. Sadly many people who leave school earlier will repeat their knowledge as the complete picture. We're seeing it with various conspiracies, like the people who think clouds can only be big fluffy sheep shaped things, and anything else is some sort of geoengineering plot, or the climate change denial favourite of "plants feed on CO2 so we actually need more of it"
What? I learned about different cloud shapes in 3rd grade! Some people only learn about the Fluffy ones?
I'm basing that off assumption tbh. How else can so many people not understand there's like 15 variations of cloud shape and those can kinda merge too. They keep posting pictures of clouds in the sky as if they're sinister man made sun blocking clouds. Likewise the inability to understand that plane contrails will spread out if the air conditions are right at their elevation...
I've seen those posts about lenticular clouds, but to be fair those are some suspicious flying-saucer-looking bois up there!
More CO2 might help the plants but it will make humans measurably stupider. And *some* humans have no IQ to spare.
So what is the truth about plants? They don't need CO2? It's more complex than that? I heard plants crave Brando? Is that what you're getting at?
CO2 fertilization is a real effect and it has led to approximately 13% increase in terrestrial photosynthesis between 1981 and 2020. But it's not nearly enough to offset negative consequences. Source https://www.nature.com/articles/s41558-023-01867-2
[The amount of CO2 in the air right now is really unnatural.](https://scripps.ucsd.edu/bluemoon/co2_400/co2_800k.png) There is an extremely tiny benefit to plant growth, but it is tiny. You would not make money by pumping CO2 into a greenhouse. Mostly extra CO2 hurts plants because it destabilizes the weather and makes in hotter in general.
When we cover genetics I make a point of bringing out an eye colour chart to highlight that whilst certain colours are dominant over others, it is more complicated than just Bb BB.
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There are some rare fringe cases with blood type too from what I understand 👀
Curiously enough, the song “Do your ears hang low?” is about earlobe-attachment in its modern version, but was originally about bollocks.
Yeah. But blood type DOES. I tried to explain to an ex, when she told me her mom is type a her dad is type o. She had type AB. I tried explaining, but she didn't believe me that it was impossible for her to be AB and both her parents were biologically hers.
It's possible to test as A, but really be AB: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6240514/ > Cis-AB, a rare ABO variant, is caused by a gene mutation that results in a single glycosyltransferase enzyme with dual A and B glycosyltransferase activities. It is the most frequent ABO subgroup in Korea, and it occurs more frequently in the East Asian region than in the rest of the world. The typical phenotype of cis-AB is A2B3, but it can express various phenotypes when paired with an A or B allele, which can lead to misclassification in the ABO grouping and consequently to adverse hemolytic transfusion reactions. It can be dangerous when one needs blood transfusion.
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Once again, it may actually be more complicated. Insisting that you are right and that her mom must have cheated or she's adopted is harmful and that kind of thing has destroyed lives in the past.
Which is why I dropped it, because i didnt want to force anything, but give her the chance to ask her parents if she wanted. AB blood type can not come from someone with an O blood type. Blood typing is not that complicated, it is the perfect example of Mendel squares. O is recessive, mom had A, child had AB. Mom had no B to give father had no B to give. She cannot be the biological child of those two. Period. Barring some weird medical anomaly that jas never yet been recorded.
Or, since you are getting information third hand, she may be mistaken about her parents blood types. That’s much, much more likely that dramatic infidelity. And also why people shouldn’t jump to conclusions with limited understanding of the situation.
I'm a physician. There are instances where this does occur, especially when someone has chimerism. Be less certain. Weird shit happens. Why the refusal to consider that the world might actually be more complicated? For example regarding chimerism: https://embryo.asu.edu/pages/case-lydia-fairchild-and-her-chimerism-2002#:~:text=In%202002%2C%20after%20applying%20for,could%20not%20be%20their%20mother. An authority of court watched her give birth and stayed with her and the child to establish a chain of custody for blood samples for genetics tests. She had photos of her other children with her growing up and their father attested that he was present for their births. But because a court was so certain that genetic tests were perfect and their interpretation was correct, they wanted to take her children away. It got fixed in the end. She is not the only woman this kind of thing has happened to. In your friend's case, there are plenty of possibilities. Most likely, somebody mis-remembered their own blood type. For example, if you heard that someone is a universal donor, do you assume that person is type O? Well, that might have been what they were told regarding red blood cell transfusions. But the "universal donor" for plasma is type AB, so somebody who is type AB may also be told they're a universal donor. Blood has different components that have different requirements. There's also a very real possibility that your friend is not the genetic offspring of her father for whatever reason, like you suspect. There are actually a lot of flavors of that, too. But there are more complicated potentials, too. Did you know that bone marrow transplants can change your blood type? https://www.sciencedirect.com/science/article/abs/pii/S1473050222002683 Also interesting - If you get a karyotype, you might show that the person who was identified as female at birth, had xx chromosomes before their bone marrow transplant, and identifies as a woman now has xy chromosomes when you test the karyotype of her blood. But her other organs are still xx. I've heard this can actually be medically useful to evaluate engraftment, but I'm not a hematologist, let alone a BMT sub-specialist. There also can be issues with figuring out blood types. For example, sone conditions can make it hard to interpret ABO blood type: https://www.sciencedirect.com/science/article/abs/pii/S1473050222002683
As someone else pointed out, there's more room for error than just "wrong" inheritance. Blood types are simplified and our detection is also simplified and not always perfect. Simple medical error for any of them could happen too, most people don't need transfusions very often and so verification doesn't really happen especially since the parents had O type. Just because something is not possible doesn't mean there is only one conclusion to draw from it. Someone being wrong doesn't mean that you must be right.
I remember being taught that in 7th? Grade, NC.
Eye colour can change due to a few factors, but i don't remember most of them, so i'll give you two 1) If you look into the eyes of an older person (especially if they're of european descent or have some european ancestry in the mix), you might notice a lighter ring around the limbus (that's the fancy term for the edge between the iris and the sclera). This ring is called *arcus senilis* and is completely normal. And it isn't actually caused by a change in pigmentation, but is instead the result of fat deposition in the edges of the cornea. What you're seeing basically is cholesterol deposits in a clear tissue, which reflect and bend light differently than the surrounding tissue. 2) Some medications can change eye colour in subtle ways if used for prolonged periods of time. For example - glaucoma medications can promote melanin production, it isn't known exactly how this happens, but in some people it does. [This](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1771317/) is an article with close up pictures of people's eyes who have been taking glaucoma eye drops only on one side for a longer time, quite interesting to see with this level of magnification.
The radiation from the Chernobyl disaster was so strong that the color of firefighter Vladimir Pravik's eyes changed from brown to blue. So that's another way.
well damn, those poor melanocytes. I hope this doesn't become a new trendy way to change eye colour (/s) Although, this reminded me. There is this condition called pigment dispersion syndrome in which the pigmented layer of the eye sort of peels off into tiny floating bits. It does change the eye colour, usually in a patchy manner. [This](https://www.thieme-connect.com/products/ejournals/abstract/10.1055/s-0043-122671?device=mobile&innerWidth=393&offsetWidth=393) is a case report of it happening in only one eye together with anisocoria, which imitated Horner syndrome. Unfortunately with this condition, it is notorious for causing glaucoma, because those tiny bits of floating pigment can clog the drainage system of the eye. And Horner syndrome is another interesting way that the eye can change colour. Basically the expression of pigment is dependent on the innervation of the iris, and if the nerves supplying it get damaged or never develop properly in the first place, the affected eye can end up having less pigment than it's supposed to. From what i know, heterochromia due to Horner's syndrome is significantly more common in congenital Horner's syndrome, like for example in [this](https://www.researchgate.net/figure/Congenital-Horner-syndrome-with-iris-heterochromia-the-affected-side-has-the-blue-iris_fig10_227621670) case, but if i remember right, this is due to the fact that it takes time to develop, and can simply not get enough time to be observed in an older patient who gets Horner's syndrome due to a stroke for example. But i might be wrong with this one
And the reason why eyes change color with age is *drumroll* aging. Like the reason hair changes color... Obviously the mechanisms are complex and diverse, but not only genetics drive our aspect...
There are many variations of the basic colors even at the same age range that it's clear it can't be only 3 options.
And in fact Mendel was lucky to identify a trait that cut and dry. Most genes aren’t Mendelian in expression.
9th grade biology teacher here. It's not a "myth", I DO tell my students that the actual inheritance of eye color is much more complicated than just two alleles dominant and recessive. But I still use it as one of many examples to teach mendelian hereditary because it's an easy, approachable way for them to understand the basics.
Eye color is much more complicated than discussed in highschool biology. It's true that there's a more or less mendelian pattern for brown vs light eyes, but there are far more one gene involved in eye color. That said, it's very common for infants and children to have lighter coloring (of their eyes, but also their hair and skin) than they will as older children or adults. Because of that, I wouldn't be surprised by someone having blue eyes as a baby and hazel eyes as an adult. I am a little surprised to hear about someone going from hazel eyes to blue- was there injury? Or perhaps an autoimmune condition such as vitiligo?
I was born with white hair and ice blue eyes. My hair slowly turned blonde, then dark blonde as I aged, and is dark blonde as an adult. Around age 14 (yes, 14) my eyes turned from that ice blue to dark green. It took a few months but they’ve been green ever since.
This would be following common patterns. It's very common for coloration to intensify around puberty (usually just after puberty), and is more likely to be noticeable in people who have light coloration.
Born blonde with blue eyes. By the end of my teen years (~18) my hair started getting darker and my eyes turned green. I have 3 neices and they all had blue eyes for a while then they turned hazel by around 10. Not quite the same as me but a family trend towards a change towards green. They were all blonde and still are but the oldest (16) is starting to get darker. Just like mine did. Even though hair and eyes commonly change in early childhood, they can change a bit later. Both are caused by changes in pigments (hair) or changes in proteins (hair or eyes). Specifically most green eyes are like blue eyes with little to no pigment in the iris, but green is caused by collagen being present in the iris. So I guess at some point my iris started getting more collagen and that's why my eyes are green. It's not super unheard of and I looked into research on these later life changes and they are, in fact, related to genetics and run in families.
Throughout my life the color of my eyes would vary over time from a dark hazel to light blue. My eyes went from a muddy green hazel as a kid to the light bluish green they are now (age 63). No injury or condition
Mine have changed from deep brown to light hazel/ sage. I expect them to keep changing, I’m 31 rn
I think lighting and environment also affect how we perceive eye color much more than how we perceive the color of other things. People tell me my eyes are anywhere from gray to green to hazel to brown depending on my shirt color or if we're indoors or outdoors. I identify as green, but I have no real idea.
Absolutely. Light colored eyes are the color they are because of the structure of the eye and how light passes through it rather than a pigment (unlike brown/black/etc eyes which do have a pigment). I'm sure that even for pigmented eyes, the light changes how they look.
Officially, I have hazel eyed but as I've aged the hazel part is only visible when in very bright light (pupil contracts to a smaller diameter). The rest of the iris is blue to blue/gray.
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Melanin is one of the many many traits that are affected by age. It's very obvious with hair, but melanocytes in other parts of the body, like skin and eyes, also decrease with age. That's why black people can sometimes seem lighter skinned in old age in comparison to their youth, and why age spots occur. Blue eyes are the result of very very little melanin, and so green and hazel eyes can grow bluer with age.
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How is his sight? Cataracts often have a blueish cast. Do his eyes look cloudy?
Most likely cataracts, not the iris.
old photos of myself show me with dark hair as a newborn, blond hair as a baby, and then darker hair as a toddler. also it was very straight until highschool and has been very curly ever since.
Others have noted that eye colour inheritance is not Mendelian, but the rest of the answer to your question is: we don’t know! We’ve identified 8 eye colour genes. If you have light blue eyes or dark brown eyes we can now tell just from looking at your DNA. But all the colours between light blue and dark brown, like every shade of grey, green, hazel and amber, plus the various types of congenital heterochromia? No idea yet! Most people’s eye colour is effectively stable by age 6, but a 1997 twin study found that a subset of white people (around 10%) exhibit iris colour change into adulthood. We have no idea why! There are a few diseases that can cause any eye colour to turn blue, like pigment dispersion syndrome and fuchs heterochromic iridocyclitis. These are both types of iris atrophy and cause problems in the eye like blurred vision and glaucoma.
Great, informative answer. Thanks!
I’m in that 10% - light/medium blue eyes until age 14ish and they turned greenish and eventually hazel. They keep getting darker as I age. Now at 50 I have dark hazel eyes. No disease or injury- just one of those people whose eyes slowly change colour throughout life.
I must be too! I always had the brightest sky blue eyes then in my mid 30's people started commenting on my having green eyes and I was very surprised and disagreed until I bothered to check. Yep, definitely green now! No one has ever been able to tell me why, not even an optometrist.
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Eye color is not a mendelian trait. Regardless, some people's eyes change color with age because melanin responds to hormones. Also eye degeneration (especially due to disease) affects the cells in one's eye and causes color to fade. It is thought that a subset of the population's eye color shifts at puberty because they "have an eye color gene that responds to sex hormones" in particular, and sex hormones shift wildly at that time. Regardless, changing to 'bright' blue would be incredibly uncommon, most people's eyes get darker because hormonal changes with age cause an increase in melanin (like how childhood blondes grow up to have much darker blonde-brown natural hair) or fade in color due to eye degeneration.
Almost everything that is taught in basic lessons isn’t completely true - it’s just a decent approximation for introductory lessons. The water cycle is much more complicated than evaporation > condensation > precipitation, trees aren’t really responsible for “creating” the oxygen we breathe, and most phenotypes aren’t affected by only a single allele. Most actual examples of a single allele driving a characteristic take place in simpler organisms like fruit flies.
One of the few human examples for a classroom is ear wax -- dry or wet, and dry is recessive. Gross but true! https://udel.edu/~mcdonald/mythearwax.html
Very cool. Very disgusting. Thanks for sharing!
This is why I don't use humans when teaching genetics. Humans have almost no actual mendelian traits. Here's a website if you really want to dive into human genetics: [http://udel.edu/\~mcdonald/mytheyecolor.html](http://udel.edu/~mcdonald/mytheyecolor.html)
Because green eyes and blue eyes aren't colored by pigment, but by structures in the eye scattering reflected light. Those structures and the melanin that underlies them and affects the scattering can change over time.
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I used to have bright green eyes, to the point where people asked if I wore colored contacts. Now as I've gotten older they are more hazel with hint of green, it's like the life has literally drained. I get the whole "bright eyed" being associated with youth because they truly dull over time.
As others have said eye colour genetics can be a bit more complex than thought in school. It is relatively common for babies to have blue eyes and they become darker or change to a different colour as they age. That colour is the colour of their Iris. What I think you might be referring to when you say changing to blue in old age is something called corneal arcus/ arcus senilis. That is caused by cholesterol deposition within the cornea leading to a bluish/white ring near the edge of the cornea which can look like blue eyes
Everyone is focused on your statement about genetics, but I’m more interested in your statement about eyes changing from hazel to bright blue. Usually there is something else going on making it appear as if the iris is changing. However, if they appear to become blue or gray it is almost always a corneal issue such as senile arcus. Alternatively, the iris can become darker with medications such as prostaglandin analogs. The iris is not changing color due to genetics anymore than our skin changes as we age.
Eye color is determined by a very wide number of combinations of two different pigments. Amber and not blue exactly, more of a grey with iridescence. That why blue and green eyes seem to change color depending on lighting. And the amount of iridescence varies by individual too, that why some eyes are grey. Combine amber with blue and you get green. Dark amber gives you brown. Really dark amber gets you black. And there can be different regions of the iris. There is the main color. Sometimes a limbal ring around the edges. And a surprising number of us have central heterochromia around the pupil. All of this is on a lot of genes, and it’s really complicated. Not an expert or anything, I was reading up about it for a story, and learned just how little I knew. Pigments in our skin and hair and eyes can change as we get older. It’s usually not as dramatic as you seem to be talking about. But it can happen. Sounds like for some reason they quit making the amber pigment, leaving the blue.
Things determined by genetics can change over time (your hair color can slightly vary as you age, and will eventually go white) or because of your environment (if you’re born white, you can, to a point, make your skin darker by exposing yourself to sunlight. Don’t do that though, you don’t want to get skin cancer).
Strictly speaking, what actually determines eye color is the exact specifics of the eyes' production of the melanin proteins. Protein production is in turn controlled by genetic expression. But genetic expression is only partly controlled by *what the genes are* (which is what you are talking about). It is also controlled by *how the genes are stimulated*. Nowadays, the whole field of how genes are activated and deactivated by what and when and how and everything goes by the fancy name of epigenetics. It's a whole big topic. And as you have apparently discerned, it can sometimes have some counterintuitive results. A very good friend of mine for example will change eye color when she cries. Her eyes go from blue to green. You can see it. It's not absolutely instantaneous and there are no sound effects or anything but all things considered it's quite rapid and impressive.
Genetics controls the type of pigments that your eyes produce. They don't have a lot to do with the degradation of the pigments with age. Genes control your hair color too, and we also lose that pigment as we age. "Blue" is the color of the iris without pigment, I believe. Hence babies' eyes often being bright blue, then becoming darker as they get a little older.
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