Possible

 Gemini:

This has long been a mystery to me: one does not necessarily pass on to one's child the genes that one is oneself exhibiting. Only this does not appear to be the case for eye colour. Why is that??

It is a common observation that eye color seems to follow "stricter" rules than other traits, often appearing to skip generations or "breed true" in a way that skin or hair color doesn't.

The reason for this lies in the difference between Mendelian (Discrete) Genetics and Polygenic (Continuous) Genetics.

1. The "Mixing" vs. "Switching" Effect

Most human traits, like height or skin tone, are polygenic. They are controlled by dozens or even hundreds of different genes that act like "volume sliders." When two people of different heights or skin tones have a child, the result is often a "blend" because the child inherits a random mix of those sliders.

Eye color, however, is dominated by a few specific "switches." While there are about 16 genes involved in eye color, two genes located right next to each other on chromosome 15 (OCA2 and HERC2) do about 90% of the work.

HERC2 acts as the master switch.

OCA2 is the pigment factory.

Because just a couple of genes have such a high "weighted vote," eye color behaves more like a digital signal (On/Off) rather than an analog signal (Blending).

2. Recessive Genes: The Hidden Blueprint

The mystery of why we don't always pass on the genes we exhibit is solved by understanding that every person carries two versions (alleles) of every gene—one from each parent—but only the "dominant" one is visible.

Brown eyes are generally dominant. You only need one "Brown" allele to have brown eyes.

Blue eyes are recessive. You need two "Blue" alleles for them to show up.

If you have brown eyes but carry a "hidden" blue allele (inherited from a grandparent), you are a carrier. You don't "exhibit" the blue gene, but you have a 50% chance of passing that blue blueprint to your child. If your partner is also a carrier, your child can inherit a "Blue" allele from both of you, resulting in a blue-eyed child from two brown-eyed parents.

3. Why Skin and Hair are Different

Skin and hair are far more "blendy" because they lack a single master switch.

Skin Color: There isn't one "dark" or "light" gene that can stay hidden for generations in the same way. Since so many genes contribute small amounts of pigment, the child's tone usually falls somewhere on a spectrum between the parents.

Eye Color: Because the HERC2 mutation is a "broken" switch (it literally breaks the ability to put pigment in the iris), it stays "broken" as it moves through generations. It doesn't dilute; it’s either there or it isn't.

4. The "Mystery" of Green and Hazel

You might wonder why, if it's just a switch, we have green or hazel eyes. This is where the other 10% of the genes come in.

Green eyes happen when the "Brown" switch is off (blue base), but a separate gene for a yellow-toned pigment called lipochrome is turned on. Blue + Yellow = Green.

Hazel eyes occur when the "Brown" switch is only partially turned on, leading to a mix of brown and green.

Because eye color relies on these specific genetic "breaks" and "switches," it feels much more like a predictable lottery than the gradual blending we see in other human features.

Are you looking at this from a family history perspective, or are you more interested in the specific molecular biology of how the HERC2 switch works?

Can two blue-eyed parents have a brown-eyed child?

The short answer is yes, although for a long time, high school biology textbooks taught that it was impossible.

Under the old "Mendelian" model, it was assumed that blue was a pure recessive trait (bb) and brown was dominant (B). Since two blue-eyed parents would only have "b" genes to give, it was thought they could only produce "bb" (blue-eyed) children. We now know that eye color is much more complex.

1. The "Broken Switch" vs. The "Empty Factory"

As we discussed, eye color is controlled by multiple genes. The two most important are HERC2 and OCA2.

HERC2 is the "master switch" that tells the body to turn on the pigment factory.

OCA2 is the "factory" that actually produces the brown pigment (melanin).

For a child to have brown eyes, they need both a working switch and a working factory. If a parent has blue eyes, it could be because their "switch" is broken, even if their "factory" is perfectly functional.

2. How the "Impossible" Happens

Imagine two blue-eyed parents:

Parent A has a broken switch but a working factory. Their eyes are blue because the factory never got the signal to start.

Parent B has a working switch but a broken factory. Their eyes are blue because there is no machinery to make the pigment.

If their child inherits the working switch from Parent B and the working factory from Parent A, the child will have both components necessary to produce melanin. The result? A brown-eyed child from two blue-eyed parents.

3. Oculocutaneous Albinism and Eye Color

In some cases, a parent might carry genes for a very mild form of albinism or other genetic variations that suppress pigment in the eye so completely that they appear blue-eyed, even if they technically carry "brown" genetic information. When combined with the DNA of a partner, those suppressed "brown" traits can be "unlocked" in the next generation.

4. Variations in "Blue"

It is also important to note that many eyes labeled "blue" actually contain small amounts of brown or yellow pigment (seen as green or hazel flecks).

If both parents have "blue" eyes that are actually a very light hazel, they are already carrying the instructions for brown pigment.

The concentration of that pigment can increase in the child, leading to a clearly brown-eyed result.

Summary

While it is statistically rare, it is genetically possible because eye color is polygenic (involving many genes) rather than a simple "either/or" trait. The "switch" and the "factory" can be inherited separately, allowing a child to "reassemble" the tools for brown eyes that were non-functional in their parents.

Does this clear up the "logic" of the inheritance for you, or were you thinking of a specific case where this happened?

I have a grey-eyed mother, and a hazel-eyed father. My eyes are yellow-brown(a bit like a cat's). Am I possible?

You are absolutely possible! In fact, your specific combination—often described as amber eyes—is a perfect example of how eye color is a spectrum rather than just a few distinct categories.

To understand how you ended up with "cat-like" yellow-brown eyes from a grey-eyed mother and a hazel-eyed father, we can look at the specific types of pigment involved.

1. The "Amber" Secret: Lipochrome

While most discussions about eye color focus on melanin (the brown pigment), there is a second pigment called lipochrome (also known as pheomelanin).

Amber/Yellow eyes contain very little melanin but a high concentration of this yellowish, golden pigment.

This pigment is also present in many hazel and green eyes, but in your case, it is the dominant feature.

2. How the Genetics Line Up

Your parents' eyes already carry the "ingredients" for your color:

Your Father (Hazel): Hazel eyes are essentially a mixture of brown melanin and green/yellow tones. This means your father carries the genetic instructions for producing that yellowish pigment and at least a moderate amount of melanin.

Your Mother (Grey): Grey eyes are a variation of blue. They have very little melanin in the front of the iris, but the structure of the iris scatters light differently (similar to why the sky looks grey on a cloudy day instead of blue).

The Result: You likely inherited the "low melanin" genes from your mother (which prevented your eyes from becoming dark brown) and the "yellow/golden pigment" genes from your father. Without enough dark melanin to mask it, the yellow lipochrome stands out, giving you that striking amber appearance.

3. The "Spectrum" Effect

Think of your family's genetics like a paint palette:

Grey is a very diluted, scattered blue.

Hazel is a muddy mix of green, gold, and brown.

Amber (You) is what happens when you take the gold from the hazel and place it on a clearer, lighter base inherited from the grey side.

Is it Rare?

Yes! Amber eyes are considered one of the rarest eye colors in humans, occurring in roughly 5% or less of the global population. They are much more common in the animal kingdom (like cats, owls, and wolves), which is why people often make that feline comparison.

It’s a beautiful genetic "shuffling of the deck" that demonstrates exactly why eye color doesn't always result in a direct copy of the parents.