Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: bezoar on 06/06/2022 04:21:36
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My daughter and her husband are both brown eyed, yet have three out of four children with blue eyes. I attributed this to their blue eyed grandparents. But can two blue eyed parents have a brown eyed child?
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IIRC "blue eyes" is a recessive gene so unlikely to appear unless both parents OR most of the grandparents were blue-eyed. And note the word is "likely" - either outcome is possible and some people even have one eye blue and one dark.
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You can have two brown-eyed parents, who each have 1 gene for brown eyes=B, and 1 for blue eyes=b, so each parent is bB.
- The children can have combinations of: BB, Bb, bB, and bb, where B is dominant
- On average (across many such trials), the children will have 75% brown eyes and 25% blue eyes.
If you have two blue-eyed parents, they each have 2 genes for blue eyes=b, so both parents are bb.
- The children can have combinations of: bb, bb, bb, and bb, where B is dominant (but non-existant)
- On average (across even a small number of trials), the children will have 0% brown eyes and 100% blue eyes.
Of course, this is a slight simplification, as other genes and de-novo mutations also play a part in eye colour too...
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Hi.
Of course, this is a slight simplification, as other genes and de-novo mutations also play a part in eye colour too...
Yes. This is a huge issue. There should be no need for children with brown eyes to worry if their parents both had blue eyes.
Quite often blue eyed people do have flecks of brown or colour in the Iris, an indication that something may have happened to suppress the brown pigment during development or as a result of an interplay with a variety of other genes, even though a dominant B gene was there. Even where there are no flecks of colour this sort of thing can still happen.
So the simple answer with dominant B and recessive b alleles is what they will want for a school level exam question but should never be worried about too much in real life.
Best Wishes.
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I used to have a GF with central heterochromia: green eyes with a brown fringe around the pupil. Mine are blue, I don't know what colour eyes our child would have had if we'd had one.
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Evan_au, I thought like you. But Eternal Student inspired me to more research and he or she is correct. Apparently, there’s more than Bb genes that determine eye color, and while it’s unusual, blue eyed parents can, in fact, have a brown eyed child. Thanks for the input to both of you.
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But can two blue eyed parents have a brown eyed child?
Only impossible in Agatha Christie novels.