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

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’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.

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.

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

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

Sounds like the blue is dominant gene compared to the brown

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

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

Genes are fascinating!

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 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!

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.

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.

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!

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 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

One in sixteen if the mother has blue eyes.

One in 256 if the mother has brown eyes.

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.

Genetics are funny, my eldest has hazel eyes like me , middle child brown like Dad. Twins have blue eyes like nobody else in the family.

My mother has hazel eyes, my dad's are green my sister's are brown and light blue, my brother has dark blue , mine are grey green !

There is so much bad statistics being spouted in this thread ... jesus wept.

It's to do with dominant and recessive genes.

There is a certain way you can get each eye colour and some genes are always recessive (can't remember off the top of head as gcse science was decades ago 🤣)

But basically there are percentage chances of each outcome but they aren't dependent (that's more maths and statistics)

So if B = brown (dominant gene) and b = blue (recessive gene)

She could be bb and he could be Bb.

So the outcomes are

bB (brown)
bb (blue)
bB
bb

So basically each child has a 50% chance of blue eyes irrespective what the previous child has.

Or at least that's what I remember from GCSE science!

I'm much more clued up on autosominal dominant gene faults as my son has a genetic condition.

My dh is brown his parents brown , green , sibling green , I'm blue as is my parents and sibling. My ds has like green/ Hazel eyes. He's neither one colour or the other. His eyes changed colour quite Late as well around 15 months, up until then they were blue. It's fascinating how it works but genetics in general are fascinating

Presumably because none of his family have had children with a person with only blue genes.

I have green eyes, my DH had blue eyes. Both sets of our parents, blue eyes. But I have native American in my genetic history and have two brown eyed children (plus one blue eyed). They are undoubtedly my DH's. My brown eyed DD has one brown and one blue eyed children. My blue eyed GC has the same unusual blue that my Mother had.

I have blue/grey eyes, husband brown, two children with blue/grey, one green/hazel - he is also left handed/footed and to his disgust, I've passed my right footedness to them all! ⚽️ I must have strong genes 🤣