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2 blue eyed children

2 blue eyed children



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My husband had light brown eyes. His father had hazel and his mother, light brown as well. His younger brother however, has blue eyes. Both my children have blue eyes. Is this possible? I thought once the recessive gene was used in my first child, his dominant brown gene would take over?


There is some chance for that. Look at this chart with some probabilities:

Its from this webpage, which also gives some background information. There is also an online calculation tool available, which takes the grandparents into account as well. It can be found here.


2 blue eyed children - Biology

We all have heard how we get certain traits from our parents such as the color of our eyes or how tall we are. These traits are passed on by genes in our DNA. Half of our DNA comes from our mother and half from our father.

Scientists have discovered that genes are inherited in certain patterns. What genes your parents and grandparents have, affects what genes you have. On this page we will learn how those patterns work.

We learned some of the basics about inheritance on the Mendel and Inheritance page. You can also go to our DNA page and our chromosome page to learn more.

A few things you should know about genes and inheritance:

Gene - Inside the DNA molecule are sections of information called genes. Each gene tells the cell how to make a certain protein which may determine a trait such as the color of the eyes.

Allele - While the section of DNA is called a gene, a specific pattern in a gene is called an allele. For example, the gene would determine the hair color. The specific pattern of the hair color gene that causes the hair to be black would be the allele.

Dominant and Recessive Genes

Each child inherits two genes for each trait from their parents. Some genes are more dominant than others. For example, brown eyes are dominant over blue eyes. If someone has a brown eyed gene and a blue eye gene, they will have brown eyes. They will only have blue eyes if both genes are blue.

The brown eyed gene is called the dominant gene and the blue eyed gene is the recessive gene.

Writing out the Genes

In order to write out the specific allele a person has for a gene, you write a letter representing the gene from the mother and a letter for the gene from the father. Dominant genes are written with capital letters and recessive genes with lower case letters. Here is an example:

  • Bb - one brown gene, one blue gene (this person will have brown eyes)
  • BB - both brown genes (this person will have brown eyes)
  • bb - both blue genes (this person will have blue eyes)

The main way to figure out the pattern of inheritance that could come from two parents is using a Punnet square. A Punnet square shows all the possible combinations of genes from the parents.

We will use the example of a plant that could have a purple flower or a white flower. The purple gene is dominant and we write it "P." The white gene is recessive, so we write it "w." Here is an example of a Punnet square where one parent has two purple genes "P" and the other parent has two white "w" genes.

Each child has the same gene pattern "Pw". They all have the dominant P gene and will all have purple flowers.

Here is another example where each parent has a purple gene and a white gene (Pw):

In this case, you can see that 75% of the children will have a dominant "P" gene and will have a purple flower. However, 25% of the children have "ww" genes and will have a white flower.

More Punnet Square Examples

In this example, one parent is PP and the other Pw.

All of the children will have purple flowers, but because one parent has a recessive "w" gene, 50% of the children will pass on the "w" gene.

Now look at what happens if only one parent has a single dominant P gene where one parent is "Pw" and the other "ww".

You can see that 50% of the children will have white flowers and 50% purple.


The exact color of your baby’s eyes depends on how much melanin he produces. Melanin is the pigment that colors the human body. Eye color depends on how much of it is stored in the iris.

There are many different eye colors, existing along a continuum. The least amount of melanin produces blue eyes. More produces green eyes, and even more produces brown eyes, which is the most common eye color worldwide.

Looking to learn more about your genetics and how they impact everything from your microbiome to your appearance and hormones? Our partners at Nebula Genomics can help you understand your genome, explore your ancestry, and learn about your inherited traits. Check out their offerings here.


31 Answer s

She might be adopted. That’s not a bad thing.

Captain_Fantasy ( 11439 />) “Great Answer” ( 0 />) Flag as… />¶

Eye color is not the simple decision between the brown (or green) and blue versions of a single gene. There are many genes involved and eye color ranges from brown to hazel to green to blue to…

How does eye color work? Eye color comes from a combination of two black and yellow pigments called melanin in the iris of your eye. If you have no melanin in the front part of your iris, you have blue eyes. An increasing proportion of the yellow melanin, in combination with the black melanin, results in shades of colors between brown and blue, including green and hazel.

What we are taught in high school biology is generally true, brown eye genes are dominant over green eye genes which are both dominant over blue eye genes. However, because many genes are required to make each of the yellow and black pigments, there is a way called genetic compensation to get brown or green eyes from blue-eyed parents.

MissAnthrope ( 21491 />) “Great Answer” ( 4 />) Flag as… />¶

it occurs often. read about the heredity and sweet peas.

trailsillustrated ( 16794 />) “Great Answer” ( 1 />) Flag as… />¶

Brown eyes are dominant and blue recessive. Likewise dark hair dominant and blond recessive. So other than the shading variations of eye color @MissAnthrope mentions, no—it would require a genetic mutation. I would guess your Biology teacher is looking for that understanding of dominant versus recessive genes. The reverse, tow brown-eyed brunette parents, could easily have a child with blond hair and blue eyes if each happened to contribute the recessive gene for that.

If that’s where your teacher is going, and they aren’t so high-and-mighty as to hate correction, point them to the Wikipedia Article on eye color.

ETpro ( 34557 />) “Great Answer” ( 0 />) Flag as… />¶

yes grandparents genes also count but in a lower ratio. but possible.

Just_Justine ( 6501 />) “Great Answer” ( 1 />) Flag as… />¶

The genetics you learn in high school is REALLY watered down.

hug_of_war ( 10725 />) “Great Answer” ( 2 />) Flag as… />¶

Sure it is. I have some friends who both (and most of their families) have dark hair and dark eyes, and they had a very blond curly-haired, blue-eyed child. You never know what you’re going to get.

chicadelplaya ( 2218 />) “Great Answer” ( 1 />) Flag as… />¶ ETpro ( 34557 />) “Great Answer” ( 0 />) Flag as… />¶

That’s quite possible. I am Asian (Chinese-Japanese), and my sister’s husband is a handsome German fellow. She has dark hair and eyes like me, and her husband is blond with greyish blue eyes. They have two little cute children, a boy and a girl. The girl, who is younger, is a carbon copy of her pretty Mom, with dark hair and eyes, and her older brother is like his Dad, with blondish hair and bluish-grey eyes. I think genetics is a very cool thing. Sometimes what you expect is not what you get.

I have odd colored eyes——one is light brown, like my Japanese Mom’s eyes, and the other is dark brown like my Chinese Dad’s. My complexion is olive, but my sister has very fair skin like my Mom, paler than some white people.

MRSHINYSHOES ( 13966 />) “Great Answer” ( 2 />) Flag as… />¶

I know a couple who are both brown eyed and dark haired and they had a little blond, blue eyed baby girl. So yes, I would say it is possible.

kheredia ( 5561 />) “Great Answer” ( 0 />) Flag as… />¶

The dark combo is dominant so often pass recessive genes and have fair children. It’s the other combination she’s asking about, which is more rare. My ex-husband is dark haired with brown eyes and both parents have blue eyes. We thought she may have fooled around- she may not have been horrid back then.

faye ( 17839 />) “Great Answer” ( 1 />) Flag as… />¶

Sure. As long as one of them fools around.

Seriously, I have five daughters, two platinum blonde with blue eyes, one dark honey blonde with hazel eyes and two brunettes. I have dark brown eyes and hair (until chemo turned it white) and my wife brunette with blue eyes. My eyes were blue until I was about eight years old – went dark then. All of my children were born with blue eyes – as I believe is normal. And yes, they are all mine – they all look like members of my own family, not my wife’s.

DarkScribe ( 15490 />) “Great Answer” ( 0 />) Flag as… />¶

Yes, and it’s simple Mendellian heredity. Just because the parents lack a certain trait, that doesn’t mean that the offspring can’t have it. Some genes are more recessive than others and/or may only express themselves in combination with certain other genes, but it is entirely possible.

Now, did any of that girl’s grandparents have blue eyes? What about the great-grandparents? Their parents? And their parents? If any of her biological ancestors had blue eyes, then it’s possible for her to inherit them.

The only way it would be impossible is if none of her ancestors since the dawn of humanity had those traits, and considering how much interbreeding has occurred lust in the last 100 generations, I think you can see how unlikely that is. By the same token, those who go on about racial purity often have at least one ancestor of another race in their own lineage, making them hypocrites. This is especially true of Americans. Personally, I have at least four different types of European blood and at least 1/64 native American.

jerv ( 31051 />) “Great Answer” ( 1 />) Flag as… />¶

Of course it’s possible. Didn’t you take 6th grade science yet?

davidbetterman ( 7550 />) “Great Answer” ( 0 />) Flag as… />¶

To have blue eyes, you must have a blue-eye gene from both parents. That’s because it’s recessive. So blue-eye genes are all you’ve got. And thus they’re all you have to give.

Now if you marry someone who also has blue eyes, the only genes you can both give to your kids are blue-eye genes. So—your kids have blue eyes.

Parents with dark eyes can carry blue-eye genes. As long as they both give their blue-eye gene to their kids, the kids of dark-eyed parents can have blue (light-colored) eyes.

So the fact that two dark-eyed parents can have light-eyed children does not prove that two light-eyed parents can have dark-eyed children.

Jeruba ( 51652 />) “Great Answer” ( 3 />) Flag as… />¶

regressive genes? Lol biology is fascinating because you never know what can come out of someone. I think almost anything is possible because life always finds ways to throw stuff out that you don’t expect.

Tenpinmaster ( 2920 />) “Great Answer” ( 0 />) Flag as… />¶

ya why not. I know two dark hair people with a red head, Stuff do skip generations ya know

jamcanfi74 ( 444 />) “Great Answer” ( 0 />) Flag as… />¶

Taken from said study “But now, “contrary to what used to be thought, we’ve discovered it is possible for two blue-eyed parents to have a brown-eyed child,” said lead author Rick Sturm, “though that is uncommon.”

tragiclikebowie ( 4805 />) “Great Answer” ( 3 />) Flag as… />¶

Sure. My dad had green eyes, my mom had brown eyes. Three girls, one had brown eyes, us other two wound up with very blue eyes.

Val123 ( 12709 />) “Great Answer” ( 0 />) Flag as… />¶

@tragiclikebowie, I see that, but this statement in the next paragraph leads me to wonder about the comprehension of the author of the article:

Until now, brown-eyed fathers might have used the trait as a simple genetic test to confirm whether or not blue-eyed children were really their own.

That false and misleading statement reflects such a gross failure to grasp even the traditional concept that it casts the report in doubt as far as I am concerned. This article is, after all, not the work of the scientist (Sturm) but of a writer of popular science material (Wood), to judge from the context. In interview articles, misquotation occurs easily, and misinterpretation even more easily than that. The interviewer is not the subject matter expert.

Taking Sturm’s statement at face value, I think we must allow the remote possibility of a dark-eyed child as the issue of two light-eyed parents, granting that it is very rare. But there is nothing unusual about the reverse—it happens all the time.

Jeruba ( 51652 />) “Great Answer” ( 1 />) Flag as… />¶

Just between my mother and her five biological siblings, there are three different hair colors, and three different eye colors, and my eye color is different from any of them and from my father while my hair color is the same as my father. Now, if we can get siblings with different traits, no two having the same eye and hair color then throw in another person with different genes and wind up with something different from any of them

Don’t forget that genetics is not completely understood yet, especially since some things require a combination of genes as well as a factor of randomness. If it was simple addition then my mother would have the same combination of colors as at least one of her siblings!

jerv ( 31051 />) “Great Answer” ( 0 />) Flag as… />¶

@tragiclikebowie The eye color issue is more complicated than a single set of genes. THere are a series that control, so it is quite possible for two bue-eyed partent to have a biological child that has brown eyes. Not common, but possible. But add to that the fact both parents are blond haired, and had a brown haired child, not within the realm of probability. It would have to be a genetic mutation. More likely, it’s not their biological child.

ETpro ( 34557 />) “Great Answer” ( 3 />) Flag as… />¶

One thing that is overlooked here is that people can adopt children that have the same hair/eye color as them as well.

Also, how improbable are we talking here? If the odds of two blue-eyed blondes having a dark-eyed brunette are comparable to being hit by lightning (around 1:600,000 IIRC) then there is a chance (though not a certainty) that the “parents” are adoptive rather than biological.

If, on the other hand, the odds are 10% (to pick a number) then they considerably exceed the odds of me making a typo, yet that is a common enough occurrence that when it does happen, it really doesn’t mean anything.

I won’t even get into the issue of why it matters if they are adopted or not since the original question was, “Is it possible…?”, except to say that if you feed me, house me, and love me for a couple of decades and I will call you Mom/Dad regardless of biology!

jerv ( 31051 />) “Great Answer” ( 0 />) Flag as… />¶

Say the blue eye allele is called e and it is recessive. Let’s say E is the brown eye allele. We know it is dominant. Therefore, both parents must have ee to have blue eyes. So without a mutation of that allele, the probability on that base pair is Zero of having a brown-eyed child. However, other genes can impact eye color, so the probability becomes small, but there. Just guessing, but it might be 1 in 1000 or less.

But the hair is more straightforward. If B is the dominant allele for brunette hair and b is the recessive allele for blond, then both parents are clearly bb and that’s that. The probabllity is Zero of them having a brunette child unless there is a mutation of that specific allele. So multiply the probablitties and you are looking at something like winning the big game lottery with the same number 10 times in a row. It’s so unlikely as to be unworthy of consideration.

ETpro ( 34557 />) “Great Answer” ( 1 />) Flag as… />¶

@ETpro If we assume that it’s just a certain gene that controls such things (as opposed to a certain combination) then I agree with you totally, and even if Nature truly is as unknown as my skeptical mind thinks it is, you make a strong case. (+1 GA to you!)

Maybe it would be a little easier for me to swallow if I hadn’t seen so many fucked-up, highly improbable things in my life, but I think that the last paragraph of my previous post renders it effectively moot anyways (at least in my mind) so I’ll go be a nay-saying bastard somewhere else now that you’ve put me in my place here :)

jerv ( 31051 />) “Great Answer” ( 0 />) Flag as… />¶

See the posts above -it is more than one gene.

faye ( 17839 />) “Great Answer” ( 1 />) Flag as… />¶

One of my sisters has blue eyes, her husband has blue eyes, two of her children have blue eyes, one hazel and the other brown. It isn’t that uncommon. My wife has blue eyes, both her parents and grandparents on both sides have brown. The parent’s eye colour is indicative of the probability of a child’s eye colour, not of the certainty.

DarkScribe ( 15490 />) “Great Answer” ( 0 />) Flag as… />¶

@faye – Exactly.. it’s not simply one gene controlling color, it has to do with shading of black and yellow in the iris. (read the explanation I linked)

MissAnthrope ( 21491 />) “Great Answer” ( 0 />) Flag as… />¶

@faye Not so. The posts above correctly stated that eye color is complicated because a number of alleles are involved. When it comes to hair color, there are only two genes controling it. One is the Brown/Blond in which, as I stated, Brown is dominant and Blond is recessive. The other controls Red, and isn’t in this picture. So in this particular case, it is that simple.

ETpro ( 34557 />) “Great Answer” ( 0 />) Flag as… />¶

I wasn’t qued in on the hair- just glance reading. I know nothing much about the hair and i’m still a little iffy about dark brown eyes from 2 blue eyes, too, alleles and all. I’ll give you hazel eyes, but I need the DNA for believing brown from blue.

faye ( 17839 />) “Great Answer” ( 0 />) Flag as… />¶

Genetics are a funny thing Both of my parents had very dark hair my paternal grandmother had blonde hair like me my brother and sister have black hair My mother before she passed away told me that after i was born that she was worried that my dad would think the worst when he saw that i was blonde his father also had black hair well he wasaway for work when i was born they called him to tell him that i had arrived mom told me that he walked into her hospital room carrying me as happy as could be and she told me that she pointed our the hair color and he said something like i know its really pretty isnt it and she said your not mad and he said why should i be and she said because people were talking and he said well my mother had hair the same color and i ended up being the living image of my paternal granmothe in fact my father always carried a picture of both me and my paternal grandmother and when people would make comments he would show them the pictures and say theres your dna test

darlenebolding ( 6 />) “Great Answer” ( 1 />) Flag as… />¶

The Scientific Reason Brown-Eyed Parents Can Have Blue-Eyed Kids

Do you have blues eyes? (Lucky you!) Are you dating someone with blue eyes? (Even luckier!) You may think the eye color similarity is no different than dating someone with a similar hair color or skin tone, but science just revealed that all people with blue eyes are genetically linked.

Thus, you and your blue-eyed hunny are both related somehow. And even weirder, your shared relative can be narrowed down to one ancestor.

A study at University of Copenhagen found that because blue eyes are a genetic mutation — before said mutation, everyone in the world had brown eyes — and everyone who has blue eyes is related.

They recruited 800 people with blue eyes and found that 99.5% (. ) of them had the same mutation in the gene that affects the color of their eyes.

But how can this be? Well, put on your biology caps because the answer is super simple: it's because of genetic mutations. And it's these genetic mutations that often have parents with blue eyes wondering how their child has brown eyes.

Buzzfeed recently released a video that details how this is possible by breaking down the science behind genetics.

There are two main genes responsible for eye color: HERC2 (HECT And RLD Domain Containing E3 Ubiquitin Protein Ligase 2) and OCA2 (oculocutaneous albinism II). HERC2 activates the OCA2 gene, and OCA2 activates proteins that act as pigments. If there's a mutation in either gene, the chain is broken and OCA2 won't produce pigments, resulting in blue eyes.

So, how is it possible to have a brown-eyed child when one or both parents have blue eyes?

Everybody inherits two genes from their parents — one from their mom and one from their dad. If the dad has one mutated gene (shown as the broken light bulb here) and one working OCA2 gene, the child will still have brown eyes because they'll inherit the dominant gene: brown eyes.

But let's say that both parents have a mutated gene.

If this is the case, there's a 25 percent chance the baby will have blue eyes. And this gene can be passed down through generations, as it's a submissive gene. This is the same concept as Punnett squares that you learned in middle school biology.

Science isn't totally sure who the relative is that blue-eyed people share, but the oldest remains of a blue-eyed person was found in Spain. The man is about 7,000 years old and had a combination of African and European genes. This means that different eye colors appeared in humans before different skin tones. Wow.

See, your dad isn't the mailman after all! But the bad news is: if you and your significant other both have blue eyes, you're distant relatives.


How Brown-Eyed Parents Can Have Blue-Eyed Kids

Do you have blues eyes? (Lucky you!) Are you dating someone with blue eyes? (Even luckier!) You may think the eye color similarity is no different than dating someone with a similar hair color or skin tone, but science just revealed that all people with blue eyes are genetically linked.

Thus, you and your blue-eyed hunny are both related somehow. And even weirder, your shared relative can be narrowed down to one ancestor.

A study at University of Copenhagen found that because blue eyes are a genetic mutation before said mutation, everyone in the world had brown eyes and everyone who has blue eyes is related.

They recruited 800 people with blue eyes and found that 99.5% (. ) of them had the same mutation in the gene that affects the color of their eyes.

But how can this be? Well, put on your biology caps because the answer is super-simple: it's because of genetic mutations. And it's these genetic mutations that often have parents with blue eyes wondering how their child has brown eyes.

Buzzfeed recently released a video that details how this is possible by breaking down the science behind genetics.

There are two main genes responsible for eye color: HERC2 (HECT And RLD Domain Containing E3 Ubiquitin Protein Ligase 2) and OCA2 (oculocutaneous albinism II). HERC2 activates the OCA2 gene, and OCA2 activates proteins that act as pigments. If there's a mutation in either gene, the chain is broken and OCA2 won't produce pigments, resulting in blue eyes.

So, how is it possible to have a brown-eyed child when one or both parents have blue eyes?

Everybody inherits two genes from their parents — one from their mom and one from their dad. If the dad has one mutated gene (shown as the broken light bulb here) and one working OCA2 gene, the child will still have brown eyes because they'll inherit the dominant gene: brown eyes.

But let's say that both parents have a mutated gene.


All photos: Buzzfeed

If this is the case, there's a 25 percent chance the baby will have blue eyes. And this gene can be passed down through generations, as it's a submissive gene. This is the same concept as Punnett squares that you learned in middle school biology.

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Science isn't totally sure who the relative is that blue-eyed people share, but the oldest remains of a blue-eyed person was found in Spain. The man is about 7,000 years old and had a combination of African and European genes. This means that different eye colors appeared in humans before different skin tones. Wow.

See, your dad isn't the mailman after all! But the bad news is: if you and your significant other both have blue eyes, you're distant relatives.


Blue-eyed humans have a single, common ancestor

New research shows that people with blue eyes have a single, common ancestor. A team at the University of Copenhagen have tracked down a genetic mutation which took place 6-10,000 years ago and is the cause of the eye colour of all blue-eyed humans alive on the planet today.

What is the genetic mutation

"Originally, we all had brown eyes," said Professor Hans Eiberg from the Department of Cellular and Molecular Medicine. "But a genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a "switch," which literally "turned off" the ability to produce brown eyes." The OCA2 gene codes for the so-called P protein, which is involved in the production of melanin, the pigment that gives colour to our hair, eyes and skin. The "switch," which is located in the gene adjacent to OCA2 does not, however, turn off the gene entirely, but rather limits its action to reducing the production of melanin in the iris -- effectively "diluting" brown eyes to blue. The switch's effect on OCA2 is very specific therefore. If the OCA2 gene had been completely destroyed or turned off, human beings would be without melanin in their hair, eyes or skin colour -- a condition known as albinism.

Limited genetic variation

Variation in the colour of the eyes from brown to green can all be explained by the amount of melanin in the iris, but blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes. "From this we can conclude that all blue-eyed individuals are linked to the same ancestor," says Professor Eiberg. "They have all inherited the same switch at exactly the same spot in their DNA." Brown-eyed individuals, by contrast, have considerable individual variation in the area of their DNA that controls melanin production.

Professor Eiberg and his team examined mitochondrial DNA and compared the eye colour of blue-eyed individuals in countries as diverse as Jordan, Denmark and Turkey. His findings are the latest in a decade of genetic research, which began in 1996, when Professor Eiberg first implicated the OCA2 gene as being responsible for eye colour.

Nature shuffles our genes

The mutation of brown eyes to blue represents neither a positive nor a negative mutation. It is one of several mutations such as hair colour, baldness, freckles and beauty spots, which neither increases nor reduces a human's chance of survival. As Professor Eiberg says, "it simply shows that nature is constantly shuffling the human genome, creating a genetic cocktail of human chromosomes and trying out different changes as it does so."

Story Source:

Materials provided by University of Copenhagen. Note: Content may be edited for style and length.


This is why it looks like blue eyes change color

If you are the lucky owner of a set of cobalt peepers, chances are you've noticed that your eyes appear to change color, sometimes looking bluer or grayer — or even lighter or darker. That was certainly the case with the famous movie actress Elizabeth Taylor, whose bright blue eyes could look violet when the light hit them just right.

There's a reason blue eyes appear to change color, which is related to why they look blue in the first place. You guessed it: It all depends on how much light is both coming into and reflecting out of the eye, according to the American Academy of Ophthalmology. Additionally, the color of the eye can look different depending on the color of clothing that a person wears, as well as the color and style of makeup that's applied around the eye.

To be fair, people with green and hazel eyes are also prone to seemingly color-changing irises as well, so this isn't unique to blue-eyed folks. But it's notable nonetheless.


What Determines Eye Color?

  • Homozygous And Heterozygous
    Human beings have two copies of every gene. One is inherited from the mother, and the other from the father. Homozygous means that two copies match or are dominant (denoted by two capital letters such BB) and heterozygous means that the two copies of the gene differ or recessive (denoted by two small letters, bb).
  • Dominant Eye Color
    Brown and green are dominant eye colors. There is 75 to 95% chance of the baby getting brown or green eyes if both the parents have same colored eyes.
  • Recessive Eye Color
    Blue is a recessive eye color. It’s highly unlikely for a baby to have blue eyes if both the parents have brown eyes.
  • Genotype
    The genotype is the gene combination for a given trait, which, in this case, is the eye color. The mother and father’s genotype will determine the eye color of the children.
  • Phenotype
    The phenotype is the physical appearance of the genotype, which in this case is the eye color.

Genotypes & Phenotypes

Alleles are alternatives of one gene. For example brown hair or blonde hair or brown eyes and blue eyes.

These are the same gene but just differ in how they are expressed. Some alleles are dominate or recessive to each other. The blue eye allele is recessive to the brown eye allele. For a person to have blue eyes, they must have two blue eye alleles.

A brown eyed person has either one allele for brown eyes or two. They can carry the blue eye but it is not expressed.

Other alleles are more complex. Some are co-dominate. The best example of this is the ABO blood type. A and B are co-dominate and O is recessive.

In the image above, each letter stands for an allele of one gene. A is the dominate allele of the gene and a is the recessive allele of the gene. It doesn't matter how they are written, AA, Aa, or aa are all possible expressions of one gene.

You would get one from your father and one from your mother.

If these stood for eye color, a person with BB (brown eyes) would have two copies of the dominate gene and have brown eyes. He would not give any other color to this children except B (brown).

A person with Bb (brown eyes) would show the dominate color but would have a recessive copy that would not show. This person could give B or b to his children. If the other parent also was Bb, it would be possible for a certain number of children to have blue eyes even though both parents have brown eyes.

A person with bb (blue) would have the recessive eye color. They could only give b (blue) to his children.

You can see that the probabilities are 3 to 1 (Brown to blue).

These are by chance and the couple could have all Brown eyed children or 2:2 or all blue eyed children.


Related Biology Terms

  • Dominant – Having the ability to mask the effects of a recessive allele.
  • Recessive – An allele that only shows phenotypic effects in the presence of another recessive allele.
  • Heterozygous – A genotype containing two types of alleles.
  • Homozygous – A genotype containing one type of allele.

1. Two hedgehogs with the genotypes “AA” and “Aa” reproduce a large litter of offspring. What is the estimated genotypic ratio of the offspring?
A. 1AA : 2Aa : 1aa
B. 2AA : 2Aa
C. 3AA : 1Aa

3. Albinism is another trait caused by a homozygous recessive genotype. Albinism is the inability to produce melanin, a pigment that colors our hair, skin and eyes. Many animals use melanin, and many animals can experience albinism. However, to produce a phenotype of albinism, two recessive non-functioning alleles are needed. In wild populations albinism is seen in relatively low numbers, a consequence of natural selection against it, and its recessive nature. Why then do we have entire populations of lab rats that are entirely albino, meaning the entire population contains recessive alleles?
A. Scientist release non-white rats into the wild.
B. These rats were genetically engineered to be white.
C. Only white rats were used, therefore only white alleles got added to the gene pool.