How can a mixed race baby have blue eyes?
January 6, 2018 3:35 PM Subscribe
If a mixed race child has blue eyes in infancy, does that mean both parents must absolutely have the blue eye gene? (One parent is full Asian.)
A recent conversation with a friend led me to be a bit curious about how eye colour works in genetics. She has a green eyed child and while she knows she is full Asian and her husband is half-Caucasian, half-Japanese, the presence of green eyes must mean she has that gene somewhere in her background, correct? She decided to do one of those home genetic testing kits and is awaiting results.
While talking to her, my curiosity piqued. I was reminded my son (whose father is Caucasian and I, myself, am full Asian) had very dark steel grey-blue eyes for the first few months of his infancy. At the time, the family doctor said it was the recessive gene just showing through in his infancy and it would likely change (they did and they are now hazel). I know this is extremely common for full Caucasian babies. But for him to even have that phase, could that mean that the blue eye gene is in my side as well? (Totally, fully Asian to my knowledge.) Or is this one of those things that my husband's gene is showing through for a bit, regardless of my side. The only thing I took away from grade 12 Biology class was that both parents need the blue eye gene for it to show up entirely. I read through a brief online search that eye colour has those rules, but it's not simple and there can be just plain anomalies.
I was hoping a science professional, who just plain knows, would be able to provide some insight.
For various reasons, I won't be doing one of those home genetics testing kits, which I know, would get aaall the answers i need :P I'm just curious!
A recent conversation with a friend led me to be a bit curious about how eye colour works in genetics. She has a green eyed child and while she knows she is full Asian and her husband is half-Caucasian, half-Japanese, the presence of green eyes must mean she has that gene somewhere in her background, correct? She decided to do one of those home genetic testing kits and is awaiting results.
While talking to her, my curiosity piqued. I was reminded my son (whose father is Caucasian and I, myself, am full Asian) had very dark steel grey-blue eyes for the first few months of his infancy. At the time, the family doctor said it was the recessive gene just showing through in his infancy and it would likely change (they did and they are now hazel). I know this is extremely common for full Caucasian babies. But for him to even have that phase, could that mean that the blue eye gene is in my side as well? (Totally, fully Asian to my knowledge.) Or is this one of those things that my husband's gene is showing through for a bit, regardless of my side. The only thing I took away from grade 12 Biology class was that both parents need the blue eye gene for it to show up entirely. I read through a brief online search that eye colour has those rules, but it's not simple and there can be just plain anomalies.
I was hoping a science professional, who just plain knows, would be able to provide some insight.
For various reasons, I won't be doing one of those home genetics testing kits, which I know, would get aaall the answers i need :P I'm just curious!
Best answer: So, eye color is extremely complicated, genetically. It's not as easy as there being a blue-eye gene - there are a lot of genes involved.
And simplified, blue eyes aren't exactly a color -they're a lack of color (or melanin). Blue is what happens when there's very little melanin present. Most babies are born with - in general - less melanin than they'll end up with later. This means that infant skin is usually lighter than the color it will end up being (even excluding what sun will do to it), infant hair is usually lighter than the color it will be as an adult, and infant eyes are usually lighter than they'll end up being. The amount lighter varies though, and for many ethnicities with darker skin/eyes/coloring (e.g. Asians, black people), "lighter" than very dark is still pretty dark.
So it's not that your husband's gene is "showing through" (that was a weird way for your doctor to phrase it), it's that the complicated eye color gene interchange between you and your husband had your kid ending up with an intermediate eye color, and so at birth, when there was less color in general, your kid's eyes looked blue.
(This is a simplified explanation and not intended to be scientifically perfect, but might help in how you think about it).
posted by brainmouse at 4:33 PM on January 6, 2018 [22 favorites]
And simplified, blue eyes aren't exactly a color -they're a lack of color (or melanin). Blue is what happens when there's very little melanin present. Most babies are born with - in general - less melanin than they'll end up with later. This means that infant skin is usually lighter than the color it will end up being (even excluding what sun will do to it), infant hair is usually lighter than the color it will be as an adult, and infant eyes are usually lighter than they'll end up being. The amount lighter varies though, and for many ethnicities with darker skin/eyes/coloring (e.g. Asians, black people), "lighter" than very dark is still pretty dark.
So it's not that your husband's gene is "showing through" (that was a weird way for your doctor to phrase it), it's that the complicated eye color gene interchange between you and your husband had your kid ending up with an intermediate eye color, and so at birth, when there was less color in general, your kid's eyes looked blue.
(This is a simplified explanation and not intended to be scientifically perfect, but might help in how you think about it).
posted by brainmouse at 4:33 PM on January 6, 2018 [22 favorites]
Also, I wanted to add that the DNA test won't actually tell you this information, because there's no such thing as "the blue-eyed gene" that they can test for. The best they can do is tell me I have a 2/3 chance of having brown or hazel eyes. For reference, I am Caucasian, with one blue-eyed parent and one brown-eyed parent. I have medium hazel eyes. Here is the entirely of my 23andMe results for eye color:
You are likely to have dark-colored eyes.
65% of customers who are genetically similar to you have dark hazel, light brown, or dark brown eyes.
We analyzed your DNA at one genetic marker that studies have shown is associated with eye color. Your prediction is based on data from 23andMe customers who consented to research and are genetically similar to you at this marker.
About Eye Color
Eye color refers to the color of the iris, which can be blue, green, hazel, brown, or many shades in between.
Biology
Human eye color is primarily determined by the amount of a pigment called melanin in the iris. This is the same pigment that determines skin and hair color. Lighter-colored eyes have less of this pigment while darker eyes have more pigment.
Genetics
The OCA2 gene helps control the amount of melanin in the iris. A certain variant near this gene changes how active it is. In people with this variant, the OCA2 gene is less active, leading to less melanin in the iris.
posted by brainmouse at 5:10 PM on January 6, 2018 [4 favorites]
You are likely to have dark-colored eyes.
65% of customers who are genetically similar to you have dark hazel, light brown, or dark brown eyes.
We analyzed your DNA at one genetic marker that studies have shown is associated with eye color. Your prediction is based on data from 23andMe customers who consented to research and are genetically similar to you at this marker.
About Eye Color
Eye color refers to the color of the iris, which can be blue, green, hazel, brown, or many shades in between.
Biology
Human eye color is primarily determined by the amount of a pigment called melanin in the iris. This is the same pigment that determines skin and hair color. Lighter-colored eyes have less of this pigment while darker eyes have more pigment.
Genetics
The OCA2 gene helps control the amount of melanin in the iris. A certain variant near this gene changes how active it is. In people with this variant, the OCA2 gene is less active, leading to less melanin in the iris.
posted by brainmouse at 5:10 PM on January 6, 2018 [4 favorites]
My dad was solidly Indian/South-Asian (23andMe puts me at 49.8% South Asian), and my mom was Italian (according to 23andMe, very heavily Italian and almost entirely Southern European with small bits of "other" European). Dad had dark brown eyes. My mom had bright blue eyes. They had 4 kids - one with bright blue eyes, 3 with hazel green-amber-brown. I have some baby photos where my eyes looked rather blue-ish, but soon settled on hazel. I think the stuff we learned in high school biology was highly simplified, and that eye color is a lot more complicated than that. We all ended up with quite dark brown hair though, and similarly fair-yellow toned skin. Mom was blonde as a child, and her hair settled on a light brown as an adult. She was fair-rosy skinned, and dad was olive-brown with black hair.
tl;dr... genes are complicated and weird.
posted by raztaj at 5:30 PM on January 6, 2018 [5 favorites]
tl;dr... genes are complicated and weird.
posted by raztaj at 5:30 PM on January 6, 2018 [5 favorites]
brainmouse has it, and I'll add that this isn't just a mixed-race phenomenon. My family is 100% South Asian, with reliable ancestry on both sides to the mid-1600s. I had gray-blue eyes when I was born, which gradually turned light brown (and now, in my 30s, are more of a mid-brown). My maternal great-uncle had green eyes. Genetics is complex.
posted by basalganglia at 5:35 PM on January 6, 2018 [4 favorites]
posted by basalganglia at 5:35 PM on January 6, 2018 [4 favorites]
My daughter (white/Asian) also had those amazing dark gray-blue eyes as an infant; now they're golden brown. It's unlikely that my wife has any European ancestry.
posted by qxntpqbbbqxl at 6:36 PM on January 6, 2018 [2 favorites]
posted by qxntpqbbbqxl at 6:36 PM on January 6, 2018 [2 favorites]
I think the confusion here is that for a period of time ((up to the?) 80's? 90's?) eye colour was taught in highschool biology class as a classical Mendelian inheritance pattern.
Iris pigmentation (there are many sub-areas of the iris, too) turns out to be pretty complicated and involves multiple genes with expression levels that change during development..
Anecdotally, in my observation, children of mixed parentages between Western European and Han Chinese tend to have very large heterogeneity of iris phenotypes, and tend to show more drastic developmentally determined change. My sample size may simply be biased, but the only two people I personally know with mismatched iris colours (for most of their lives) were of that heritage.
There have been several significant insertions of Western alleles into the "Chinese" population over history. There are a large number of ethnic subgroups that defy political geography. The "Jade Eyed Girl" is a thing, and it's probably a rare expression of a gene from a Roman soldier with 'barbarian' origins (or sometimes a spontaneous mutation) interacting with a whole slew other more locally prevalent gene variants.
posted by porpoise at 8:02 PM on January 6, 2018 [3 favorites]
Iris pigmentation (there are many sub-areas of the iris, too) turns out to be pretty complicated and involves multiple genes with expression levels that change during development..
Anecdotally, in my observation, children of mixed parentages between Western European and Han Chinese tend to have very large heterogeneity of iris phenotypes, and tend to show more drastic developmentally determined change. My sample size may simply be biased, but the only two people I personally know with mismatched iris colours (for most of their lives) were of that heritage.
There have been several significant insertions of Western alleles into the "Chinese" population over history. There are a large number of ethnic subgroups that defy political geography. The "Jade Eyed Girl" is a thing, and it's probably a rare expression of a gene from a Roman soldier with 'barbarian' origins (or sometimes a spontaneous mutation) interacting with a whole slew other more locally prevalent gene variants.
posted by porpoise at 8:02 PM on January 6, 2018 [3 favorites]
The only two people I personally know with mismatched iris colours were... Western European / Han Chinese.
Mismatched iris colours is called heterochromia iridum. It seems to often occur due to a developmental, not inherited factor (like mosaicsm or chimerism) and therefore probably not strongly correlated to race. (Lots of famous white people, including Dan Aykroyd, Mila Kunis and Kate Bosworth have it).
posted by pseudostrabismus at 10:13 PM on January 6, 2018 [2 favorites]
Mismatched iris colours is called heterochromia iridum. It seems to often occur due to a developmental, not inherited factor (like mosaicsm or chimerism) and therefore probably not strongly correlated to race. (Lots of famous white people, including Dan Aykroyd, Mila Kunis and Kate Bosworth have it).
posted by pseudostrabismus at 10:13 PM on January 6, 2018 [2 favorites]
Response by poster: Wow… Thank you all so very much for your extremely informative responses! I learned a lot and understand how complicated this topic is now. I really was going off my a basic understanding from high school biology (definitely within the ‘90s and what porpoise mentioned), but can now see how dated that information is. Thank you, Hive Mind!
To clarify: I wasn’t really surprised the eye colour would change as my son grew out of infancy, but was more surprised that he had a lighter eyes stage entirely (when I thought they were blue). Basically, I had never thought that possible (with my archaic knowledge, I was firmly convinced my brown eyes would conquer each and every time — my older son had dark eyes from day one), so was initially teased with the thought I might have had some exciting family history ;)
My doctor likely used other language… although I swear she used the word ‘recessive’.
And the mentions of 23andme — that was the kit my friend ordered. Good to know about what you’re really told in the results! Thank you!
raztaj - your family sounds beautiful!!
posted by branparsons at 12:15 AM on January 7, 2018 [1 favorite]
To clarify: I wasn’t really surprised the eye colour would change as my son grew out of infancy, but was more surprised that he had a lighter eyes stage entirely (when I thought they were blue). Basically, I had never thought that possible (with my archaic knowledge, I was firmly convinced my brown eyes would conquer each and every time — my older son had dark eyes from day one), so was initially teased with the thought I might have had some exciting family history ;)
My doctor likely used other language… although I swear she used the word ‘recessive’.
And the mentions of 23andme — that was the kit my friend ordered. Good to know about what you’re really told in the results! Thank you!
raztaj - your family sounds beautiful!!
posted by branparsons at 12:15 AM on January 7, 2018 [1 favorite]
How Blue and Green Eyes Exist When Those Pigments Are Not Found in the Human Eye
posted by 445supermag at 2:31 PM on January 7, 2018 [1 favorite]
posted by 445supermag at 2:31 PM on January 7, 2018 [1 favorite]
Just throwing in another "eye colour is weird" anecdote; my and my 3 siblings all have different coloured eyes, even though we share the same parents.
Sister 1 = hazel; Brother = brown; Me=green; Sister 2 = blue.
posted by dotparker at 2:09 PM on January 8, 2018 [1 favorite]
Sister 1 = hazel; Brother = brown; Me=green; Sister 2 = blue.
posted by dotparker at 2:09 PM on January 8, 2018 [1 favorite]
This thread is closed to new comments.
Basically, many/most Caucasian have eyes that start out somewhere on the light blue/green/grey side of things, then settle in to their final color later.
Genetic determination of human eye color is real, but complicated. Not nearly so simple as the Punnet squares you may have drafted in high school or college. There are probably around a dozen genetic loci that control human eye color, possibly many more, though knowing a handful is enough to predict adult eye color with fairly good accuracy.
So: green eyes must mean she has that gene somewhere in her background, correct?
Well, no, assuming the infant is under one year old, and that by "gene" you mean an allele that simply codes for green eyes in an Asian lady.
It's complicated, but my understanding is that we can be confident that the infant has some euro/caucasoid alleles from dad that result in light-eyed infancy, which is extremely common among some groups of people but rare in others. Initial eye color of these babies bears no simple clear relationship to final eye color.
More info at Wikipedia here: , including genetic determination and changes over time.
I am a biologist but I am not your biologist. I am not in any way an expert on human eye color or heritability.
posted by SaltySalticid at 4:30 PM on January 6, 2018 [11 favorites]