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!

Most my friends babies have blue eyes even when one parent has brown eyes. It’s a 50/50 chance but her genes may just be a bit stronger than his.

It’s not 50/50 because blue is a recessive gene.

Sikh Punjabi = Indian in case anyone doesn’t know

Both of my parents have brown eyes, and I have blue eyes. The odds are low in my case, but it's still possible. It's a high chance in your family's case.

Both dc have blue eyes even though dh and I are brown eyed.

He more than likely has a recessive blue gene along with his dominant brown one. No need to be suspicious.

They used to think eye colour was purely determined by the dominant or recessive alleles, but now they’ve actually found around 8 genes which determine eye colour. So, it’s not as simple as we used to think.

I don't get your question. It's 50% chance of a blue eyed child each time they conceive. If I flip a non-weighted coin 20 times and it lands on heads each time, then the odds of it landing on heads on the 21st flip is still 50/50.

Haha they have jet black hair and despite being pale-ish clearly have an olive undertone from their dad.

Although eye colour is typically used when learning about genetics in science class, and about dominant and recessive genes, it's a lot more complicated than that. There are many genes that express eye colour.

Myself and dh have hazel eyes, two of our dc have hazel and one has blue. The baby is yet to be determined.

If the odds for each child are 1 in 2 then the chance of all 4 having blue eyes is 1 in 16. Not very likely but a long way from impossible.

For each child the likelihood is 50:50 if your BIL has the recessive gene for blue eyes, which he must have, however he came by it. In him it is not expressed because he also has the dominant dark brown eye gene.

(I am assuming your sister is blue eyed and is therefore passing on a recessive blue eyed trait, and obviously genes are complex so it never really as tidy as this).

If it's a 50/50 chance that a child will have blue eyes, it's a 1/16 chance that all four will.

If the dad has brown/blue genes (Bb) then he will have brown eyes because the brown gene is dominant. The mum has blue/blue genes (bb) so had blue eyes. The babies can be (Bb) or (bb).

But we wouldn't find it so surprising if someone has four children and they are all girls, which is a similar probability.

This stuff baffles me. My husband and I, as well as our parents, all have/had brown eyes and brown hair. Our three children have either blue or hazel eyes, two with dark blonde hair and one with strawberry blonde hair. 🤷‍♀️

Dad has one recessive blue gene and one dominant brown gene.
Mum has two recessive blue genes.
So, between them they have 3 genes for blue and only 1 for brown.
The children have a 2 in 4 chance of having blue eyes and a 2 in 4 chance of brown. They could have the following:
1br, 1 bl = brown
1bl, 1bl = blue

I don't know about the complexities (per @KrisAkabusi and @Theredoubtableskins ) but if you just assume the basics, which is that blue is the recessive gene, then feasibly the parents' genes could be Bl/Bl (DSis) and Br/Bl (BIL). That means the likelihood of any one child having blue eyes is 50%. All four having blue eyes is highly unlikely (I think like, 5% odds or thereabouts) but still possible.

I am the only redhead in my family across all known lines for several generations. It's a recessive gene so obviously buried somewhere on both sides.

Unfortunately what you learned today was incorrect. Eye colour inheritance is much more complicated than that. So although not as common, it is not an anomaly. My friends is Indian, her parent are both Indian, everyone has brown eyes except 1 sister who has blue eyes. Nobody else in the family has them.

Yep, assuming it's a 50/50 chance each time it's 1 in 16 as someone said earlier or 6.25% chance of having 4 in a row with blue eyes. Unlikely but absolutely possible! As someone said earlier its the same probability of having 4 girls in a row!

Well said. It's not straight forward dominant and recessive like you are told in GCSE biology.

I think it depends on the grandparents' eye colours too.

Good point.

Both DH and I have brown eyes and one DC has blue eyes and the other green-grey 🤷‍♀️

YABU as scientists now know that there are a lot more genes involved in eye colour than previously thought. It isn't just a case of BB + Bb = Bb or BB