Can someone explain chances of 4 kids with blue eyes when one parent is brown eyed?

[Korner]

Dsister (blue eyes) has 4 kids with BIL (very dark brown eyes almost black). All 4 kids (7 - 3 yo) have bright blue eyes.

BIL is Sikh Punjabi. Apparently has no history of blue eyes but says some second cousins have green eyes - not common but not unusual. My family all pretty much have blue eyes.

This has to be an anomaly. Just curious as the discussion came up at baby group today. Learned that it should only really be 50% likelihood of blue eyes if one parent has brown eyes and the other
blue.

I have one of each (brown and blue) despite DH being green eyed. I’m also blue eyed.
Genes are very interesting!

My DH has brown eyes, I have blue eyes. Our son has greeen eyes, our daughter has blue eyes, red hair and is left handed. She is so very different to all her other siblings (by different dad) and cousins.

One in sixteen if the mother has blue eyes.

One in 256 if the mother has brown eyes.

My side all bright blue
Ex was Hazel brown from his mum but his dad and brother's have dark blue
Our sons are turquoise almost

My solitary dc has blue (well, grey) eyes. His dad and I have brown eyes, and three of the four grandparents have/had brown eyes, only one is blue eyed. (This is the one who actually complained that none of her four GC had brown eyes... 🙄)

My dad had brown eyes, my mother has blue eyes. My brother has blue eyes but I have green eyes. My cousins and brother all have blond hair and blue eyes I and the only one with dark hair and non blue eyes. Genes are weird!

Sikh Punjabis are Northern Indian. The North of India has been invaded by the Persians, Greeks, Egyptians, Afghans, Chinese/Mongolians and British. It’s a very diverse gene pool.

There are a number of Northern Indians and Pakistanis incredibly light skinned with green and blue eyes. It’s likely he carries one of the genes.

Assuming that the dad has a dominant brown eye allele and a recessive blue eye allele (Bb)... and mum has two recessive blue eye alleles (bb).... then any child would have a 50% chance of blue eyes.

I am from a similar background to your BIL and my husband is white with hazel eyes. My eldest has blue eyes, middle child has brown and youngest has hazel. Blue eyes likely due to recessive gene for blue eyes and the rest is a equal share between me and husband!

There are genes that say 'be this colour'.

There are genes that say 'if X colour, modify it'

There are genes that say 'over time, alter to X colour'

There are dominant genes - you only need 1 copy to see the effect.
Recessive genes - you need 2 copies to see the effect.
There are incomplete dominant genes - so (using horse coat colour genetics as I know more about that) you would see some evidence of two different genes, say cream colour AND red colour, producing a dilute golden shade. In some flowers red is an incomplete dominant gene so a flower carrying red and white could appear pink.

And theres lots more besides - there are genes that determine patterns, telling other genes to switch off a particular pigment here, but not there (again with the horses, this is why we have horses with splashes of white over their bodies, and yet that is a different gene to the one that says 'white socks on legs and a stripe down the nose').

I have brown eyes my partner blue.
4 kids. Each have different eye colour
(Brown, hazel, blue & green)

Genes are fascinating!

Exactly that ie it can come from grand parents, great grandparents etc

Sounds like the blue is dominant gene compared to the brown

I think you need to factor in grandparents
my granny had green eyes - grandad brown eyes
I was told green eyes make brown even more dominant
All 5 grandchildren from them
have brown eyes despite having blue eyes mothers

As for the next generation- mainly blue with some green eyes
Generics are fabulous

https://www.babymed.com/tools/baby-eye-color-calculator-predictor?p1=Brown&p2=Blue

I have never understood why they teach the model of recessive and dominant genes when it's clearly obvious eyes don't work like that in real life. I mean there's lots more different shades and colours than brown and blue for starters.

I’m one of 6kids, I’m the only brown eye child. Dad and my siblings all had/have piercing blue eyes, my mum had green.
other than the fact I don’t have a beard or blue eyes I’m identical to my siblings.

Eye colour genetics is actually fairly complex. It's not true that two brown eyed parents can't have a blue eyed child, just rare! If some of his family have green eyes he's likely got a recessive blue eyed gene so with your sister having blue eyes the children can have blue eyes. It would be less than 50% chance of them having blue eyed children so all 4 having blue eyes is unusual but definitely not impossible!

I have three girls all blue eyed. Their Dad and I both have hazel / brown eyes but we both have parents with blue eyes

This isn’t how eye colour genetics works though, as explained by @KrisAkabusi

It’s not as simple as brown trumps blue.

From what I've read apparently blue is the weaker colour? My parents have a mix of blue and Hazel eyes and we have green. A friend is mixed race, predominantly Pakistani and her partner Caucasian and their kids have blonde hair and blue eyes. Another friend is Swedish, DH mixed race, predominantly Moraccon, and their kids have darker skin and brown eyes. Yes, genetics are interesting and go way back. Doesn't seem to matter what gender, present physical attributes, the strongest gene comes through? So the studies which say blue eyes are weaker are being disproven. Xx

I've got two with brown eyes and brown hair, one with greeny brown eyes and brown hair and one blonde with blue eyes. Parents are both brunette, one with brown eyes and one with blue. I love the differences :-)

I'm a ghost pale, green eyed, bright redhead

Mum is dark olive skin, dark brown eyes, almost black hair. So is the rest of the family on her side, they step outside and tan very dark
Dad is average skin tone, blue eyes, strawberry blonde

I look like a randomer that's dropped in for tea at any family gatherings

I have green eyes - a different shade to my mum. Dad has brown. His parents had brown and blue eyes.

Think my mum got green eyes from her father. She has no memory of him as he died when she was 4. Her father was 8-10 years older than his MIL. I certainly remember that my grandmother had blue eyes.

My green eyes are unusual. Smoky grey outer with brown flecks around iris. Maybe pretty to look at but looking through them - different story

Im an only child and if I had siblings they would have different colours eyes

I'm from a similar background to your BIL. I have medium brown eyes, my (Caucasian ) husband has blue eyes. Husband's dad (Caucasian) has blue eyes. Our son has blue eyes. Mother in law (Caucasian) has dark brown eyes. My daughter has dark brown eyes. My mum (Punjabi) has dark brown eyes. My dad (Punjabi) has greyish eyes. I think my dad's mum also had greyish eyes. It's complicated.

Exactly the same chance of them four girls or four boys.