Which Is Dominant Blue Or Brown Eyes?
- Pieter Maas
Why are our kids’ eyes different colours? – Let’s look at why a blue-eyed parent (dad) and a brown-eyed parent (mum) and can have brown, green, and blue-eyed children. For gene 1, OCA2, there are two possibilities: brown or blue. The brown version of gene 1 is dominant over the blue one. Dominant means that if at least 1 of your two copies is brown (Bb), then you will have brown eyes. Geneticists represent the different versions of the eye colour gene as B for brown and b for blue (the capital letter is the dominant, the lowercase, recessive).
- So brown eyes are either Bb or BB and blue eyes are bb.
- For gene 2, there are two possibilities, green or blue.
- Green is dominant over blue.
- Green eyes can be GG, or Gb, while blue eyes are bb.
- Brown is dominant over green, so if you have a B version of gene 1 and a G version of gene 2, you will have brown eyes.
The possible gene combinations that can give you brown, green, or blue eyes are shown in the chart. Back to the green or blue-eyed children. Dad can only be bb bb as he has blue eyes. Since mum has brown eyes, she could have any of six different possibilities.
What gene is more dominant blue or brown eyes?
Eye color inheritance pattern – Due to the number of genes involved in eye color, the inheritance pattern is complex. Although a child’s eye color can generally be predicted by looking at the color of the parents’ eyes, the polymorphisms that can arise mean a child may well have an unexpected eye color.
- A child’s eye color depends on the pairing of genes passed on from each parent, which is thought to involve at least three gene pairs.
- The two main gene pairs geneticists have focused on are EYCL1 (also called the gey gene) and EYCL3 (also called the bey2 gene).
- The different variants of genes are referred to as alleles.
The gey gene has one allele that gives rise to green eyes and one allele that gives rise to blue eyes. The bey2 gene has one allele for brown eyes and one for blue eyes. The allele for brown eyes is the most dominant allele and is always dominant over the other two alleles and the allele for green eyes is always dominant over the allele for blue eyes, which is always recessive.
- This means parents who happen to have the same eye color can still produce a different eye color in their child.
- For example, if two parents with brown eyes each passed on a pair of blue alleles to their offspring, then the child would be born with blue eyes.
- However, if one of the parents passed on a green allele, then the child would have green eyes and if a brown allele was present, then the child would have brown eyes irrespective of what the other three alleles were.
Chromosome 15 – Eye colour However, this does not explain why two parents with blue eyes can have a child with brown eyes. It also does not explain how grey or hazel eyes arise. This is where modifier genes, other genes associated with eye color and mutations all come into picture, as they can all lead to variability in eye color.
Can a brown eyed parent and a blue eyed parent have a blue eyed child?
A couple’s children can have almost any eye color, even if it does not match those of either parent. Currently it is thought that eye color is determined by about six genes, so you can imagine how inheritance of eye color becomes very complicated. There are some characteristics of various plants or animals that are determined by two simple genes.
Let’s think about this situation. If we say brown is dominant to blue (and we pretend that eye color is decided the way you learned it), someone with brown eyes, like your mom, may be carrying one blue allele and one brown allele (but only the brown shows up). She can pass either of these alleles on to her offspring, so in theory, even though brown is dominant, a brown eyed mom and a blue eyed dad could give birth to a blue eyed child.
Now imagine a third green allele, which is dominant to blue, but recessive to brown. If your mother carried the green allele (but only her brown shows up), she could easily pass the green allele on to you (and in terms of probability, would do so 50% of the time), and matched with your dad’s blue allele, you would have green eyes.
- This is a nice way to think about it, but again, eye color is much more complicated, and involves genes that determine the amount of pigment in your eyes, as well as genes that can modify even dominant alleles.
- The wikipedia article on this is written at a pretty advanced level, but it may help explain what is going on with eye color eye color.
Eye image by Laitr Keiows via Wikimedia Commons
Can 2 brown-eyed parents produce blue eyes?
Is it possible for two brown eyed people to have a child with blue eyes? Editor’s Note (4/14/2021): The following article and diagrams present an over-simplified, outdated version of eye color genetics. Eye color is influenced by at least 50 genes, not all of which are well understood.
Yes. The short answer is that brown-eyed parents can have kids with brown, blue or virtually any other color eyes. Eye color is very complicated and involves many genes. To begin to understand how parents with brown eyes could have blue-eyed children, let’s imagine that eye color is due to a single gene, EYCL3, which comes in two versions or alleles, brown ( B ) and blue ( b ).
Remember that for most genes (including eye color), you have two copies of each gene, and that you inherited one from your mother and one from your father. The brown version of the eye color gene ( B ) is dominant over the blue version ( b ). Dominant means that if either of your genes is the B version, then you will have brown eyes.
Genetically speaking, then, people with brown eyes could be either BB or Bb while people with blue eyes could only be bb, Example of a one-gene model for eye color. For two parents with brown eyes to have a blue-eyed child, both parents must genetically be Bb, When this happens, there is a 1 in 4 chance that these parents will have a bb child with blue eyes.
Unfortunately, eye color is not as simple as this. Besides the EYCL3 gene described above, at least two other genes, EYCL1 and EYCL2, are also involved. Although this set of genes explains how people can have green eyes, it does a poor job of explaining how blue-eyed parents could have brown-eyed children or how anyone can have hazel or gray eyes at all.
To understand green eyes in all of this, we only need to review EYCL1 and EYCL3 (EYCL2 is a poorly understood brown eye color gene). Remember, EYCL3 has two versions, brown ( B ) and blue ( b ). EYCL1 also comes in two versions, green ( G ) and blue ( b ). The way these genes work is that if you have a B allele, you will have brown eyes ( B is dominant over b and G ), if you have a G allele and no B allele, you will have green eyes ( G is dominant over b ) and if you have all b genes, then you will have blue eyes.
Example of a two-gene model for eye color. I hope this helps to answer your question. As you can tell, while some progress has been made, eye color is a very complex, polygenic trait that is not yet fully understood. : Is it possible for two brown eyed people to have a child with blue eyes?
Are dark eyes dominant?
The Genetics of Eye Color Download the PDF version of Biotech Basics: Genetics of Eye Color Countless students have been taught that a single gene controls eye color, with the allele for brown eyes being dominant over blue. Scientists now realize such a model is overly simplistic and incorrect. What you need to know:
DNA provides the set of recipes, or genes, used by cells to carry out daily functions and interact with the environment. Eye color was traditionally described as a single gene trait, with brown eyes being dominant over blue eyes. Today, scientists have discovered that at least eight genes influence the final color of eyes. The genes control the amount of melanin inside specialized cells of the iris. One gene, OCA2, controls nearly three-fourths of the blue-brown color spectrum. However, other genes can override the OCA2 instruction, albeit rarely. This multifactorial model for eye color explains most of the genetic factors that influence eye color.
Introduction In 1907, Charles and Gertrude Davenport developed a model for the genetics of eye color. They suggested that brown eye color is always dominant over blue eye color. This would mean that two blue-eyed parents would always produce blue-eyed children, never ones with brown eyes.
For most of the past 100 years, this version of eye color genetics has been taught in classrooms around the world. It’s one of the few genetic concepts that adults often recall from their high school or college biology classes. Unfortunately, this model is overly simplistic and incorrect – eye color is actually controlled by several genes.
Additionally, many of the genes involved in eye color also influence skin and hair tones. In this edition of Biotech Basics, we’ll explore the science behind pigmentation and discuss the genetics of eye color. In a future edition, we’ll discuss genetic factors that contribute to skin and hair color.
- A primer on pigmentation The color of human eyes, skin and hair is primarily controlled by the amount and type of a pigment called melanin.
- Specialized cells known as melanocytes produce the melanin, storing it in intracellular compartments known as melanosomes.
- The overall number of melanocytes is roughly equivalent for all people, however the level of melanin inside each melanosome and the number of melanosomes inside a melanocyte varies.
The total amount of melanin is what determines the range of hair, eye and skin colors. There are a number of genes involved in the production, processing and transport of melanin. Some genes play major roles while others contribute only slightly. To date, scientists have identified over 150 different genes that influence skin, hair and eye pigmentation (an updated list is available at ).
A number of these genes have been identified from studying genetic disorders in humans. Others were discovered through comparative genomic studies of coat color in mice and pigmentation patterns in fish. (A previous Biotech101 article that provides an overview of comparative genomics can be found,) figure one Eye color genes In humans, eye color is determined by the amount of light that reflects off the iris, a muscular structure that controls how much light enters the eye.
The range in eye color, from blue to hazel to brown (see figure one), depends on the level of melanin pigment stored in the melanosome “packets” in the melanocytes of the iris. Blue eyes contain minimal amounts of pigment within a small number of melanosomes. Irises from green–hazel eyes show moderate pigment levels and melanosome number, while brown eyes are the result of high melanin levels stored across many melanosomes (see figure two, left).
- To date, eight genes have been identified which impact eye color.
- The OCA2 gene, located on chromosome 15, appears to play a major role in controlling the brown/blue color spectrum.
- OCA2 produces a protein called P-protein that is involved in the formation and processing of melanin.
- Individuals with OCA2 mutations that prevent P-protein from being produced are born with a form of albinism.
These individuals have very light colored hair, eyes and skin. Non-disease-causing OCA2 variants (alleles) have also been identified. These alleles alter P-protein levels by controlling the amount of OCA2 RNA that is generated. The allele that results in high levels of P-protein is linked to brown eyes.
Another allele, associated with blue eye color, dramatically reduces the P-protein concentration. On the surface, this sounds like the dominant/recessive eye color model that has been taught in biology classes for decades. However, while about three-fourths of eye color variation can be explained by genetic changes in and around this gene, OCA2 is not the only influence on color.
A recent study that compared eye color to OCA2 status showed that 62 percent of individuals with two copies of the blue-eyed OCA2 allele, as well as 7.5 percent of the individuals who had the brown-eyed OCA2 alleles, had blue eyes. A number of other genes (such as TYRP1, ASIP and ALC42A5 ) also function in the melanin pathway and shift the total amount of melanin present in the iris.
- The combined efforts of these genes may boost melanin levels to produce hazel or brown eyes, or reduce total melanin resulting in blue eyes.
- This explains how two parents with blue eyes can have green- or brown-eyed children (an impossible situation under the Davenport single gene model) – the combination of color alleles received by the child resulted in a greater amount of melanin than either parent individually possessed.
As a side note, while there is a wide variability in eye color, colors other than brown only exist among individuals of European descent. African and Asian populations are typically brown-eyed. In 2008 a team of researchers studying the OCA2 gene published results demonstrating that the allele associated with blue eyes occurred only within the last 6,000 – 10,000 years within the European population.
- Pigmentation research at HudsonAlpha Dr.
- Greg Barsh, a physician-scientist who has recently joined the HudsonAlpha faculty, and his lab study key aspects of cell signaling and natural variation as a means to better understand, diagnose and treat human diseases.
- In particular, his work has focused on pigmentation disorders.
He has explored mutations that affect easily observable traits—such as variation in eye, hair or skin colors—as a signpost for more complex processes such as diabetes, obesity, neurodegeneration and melanoma, the most serious form of skin cancer. – Dr.
Which traits skip a generation?
How can red hair skip a generation and reappear in a family? Traits like red hair or blue eyes that skip generations can be frustrating (especially if your mailman has red hair and/or blue eyes!). But it is perfectly natural. And explainable by genetics.
Many of our traits come from our genes. There are genes that determine eye shape, hair texture, hair, eye, and skin color, etc. The traits that are most likely to skip generations are the ones caused by recessive gene versions. To understand what this means, we need to remember two things about our genes.
Are Blue Or Brown Eyes More Dominant
First, we have two copies of most of our genes – one from mom and one from dad. And second, our genes can come in different versions called alleles. These different versions can lead to different traits. Traits like red hair can skip many generations. (Image: ) For example, there are versions of the MC1R gene that lead to red hair.
And versions that don’t lead to red hair. What this all means is that people can have three possible combinations of the MC1R gene. They can have two non-red versions, two red versions, or one of each. It is pretty obvious that having two non-red versions means you won’t have red hair. And that having two red versions means you will have red hair.
But what if you have one version of each? This is where recessive comes in. Not all versions of genes are created equal – some versions are “weaker” than other ones. In genetics speak, we’d say that some alleles are recessive and some are dominant. The red hair versions of the MC1R gene are recessive to the other MC1R versions.
So if you have a red and a non-red version of the MC1R gene, then you won’t have red hair. But you carry the recessive red hair version that you can pass down to your kids. Another way to say this is that you are a carrier for red hair. Carriers are the reason why traits can skip generations. I am going to use your story as a way of explaining why this is.
Writing and saying non-red version of MC1R or red version of MC1R gets a bit tiring after a while. So I will do what geneticists do. I will call the non-red version of the MC1R gene R and the red version r, I also used that naming system in this figure: Imagine that your grandfather was a redhead and that your grandmother wasn’t a carrier.
- This would make grandpa rr and grandma RR,
- None of their kids would have red hair but they would all be carriers because grandpa would pass on his red hair gene.
- All the kids have a non-red copy of the MC1R gene ( R ) from grandma and a red copy ( r ) from grandpa – they would all be Rr,
- Let’s say one of these kids is your mother and that your father wasn’t a carrier.
In other words, your mom is Rr and your dad is RR, Your mother has an equal chance of passing either the red ( r ) or the non-red ( R ) version to her kids. Let’s say she passed the red hair version to you. Since your dad wasn’t a carrier, this means he passed only a non-red version ( R ) to you.
So you are a carrier for red hair ( Rr ). So now we have gone two generations without a redhead. Imagine that something similar happened on your husband’s side of the family. Now here you are, both carriers for red hair ( Rr ). As I said before, a carrier has an equal chance of passing either copy of a gene to his or her child.
So each of your children has a 1 in 2 chance of getting a red hair version ( r ) from you and the same chance of getting a red hair version ( r ) from your husband. To figure out the chances that you both will pass an r down to your kids, you multiply the chances together.
- This means that each child has a 1 in 4 chance of getting two r versions and having red hair.
- The chances for this happening with both your kids are 1 in 16 (again just multiplying the chances together).
- To give you some idea about how likely this is, it is about the same chance as flipping a coin four times and getting four heads in a row.
Or the same as a family having four boys in a row. Not the most common outcome but we’ve all seen families with kids of all one sex or the other. So there you have it. Recessive traits like red hair can skip generations because they can hide out in a carrier behind a dominant trait.