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Original poster

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

142 replies

Korner · 30/05/2024 19:38

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!

OP posts:
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Foldinthecheese · 30/05/2024 19:49

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. 🤷‍♀️

TheYearOfSmallThings · 30/05/2024 19:47

Spacie · 30/05/2024 19:46

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.

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

Elisheva · 30/05/2024 19:46

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).

NeverEnoughPants · 30/05/2024 19:46

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

TheYearOfSmallThings · 30/05/2024 19:46

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).

Spacie · 30/05/2024 19:46

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.

Outnumbered83 · 30/05/2024 19:46

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

KrisAkabusi · 30/05/2024 19:44

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.

Original poster
Korner · 30/05/2024 19:44

honeyfox · 30/05/2024 19:43

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

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

OP posts:
CammyChameleon · 30/05/2024 19:44

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.

Theredoubtableskins · 30/05/2024 19:43

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.

honeyfox · 30/05/2024 19:43

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

Cluelessaf · 30/05/2024 19:42

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

comedycentral · 30/05/2024 19:42

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.

Original poster
Korner · 30/05/2024 19:42

Sikh Punjabi = Indian in case anyone doesn’t know

OP posts:
Elisheva · 30/05/2024 19:42

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

Hiddenvoice · 30/05/2024 19:41

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.