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PeterMW
Saturday, March 27th, 2004, 01:49 PM
It was my belief that brown eyes were dominant over blue, so that two brown-eyed people could produce a blue-eyed baby (because they both had blue-eyed genes not represented in their phenotype), but not the reverse. However two friends of mine who have blue eyes have a brown-eyed baby. Assuming that my friend didn't cheat on her partner, how can this have happened ? The baby is 9 months old, so its eye colour is by now established, and the eyes are definitely clear brown, not hazel or dark green.

Euclides
Saturday, March 27th, 2004, 08:02 PM
It was my belief that brown eyes were dominant over blue, so that two brown-eyed people could produce a blue-eyed baby (because they both had blue-eyed genes not represented in their phenotype), but not the reverse. However two friends of mine who have blue eyes have a brown-eyed baby. Assuming that my friend didn't cheat on her partner, how can this have happened ? The baby is 9 months old, so its eye colour is by now established, and the eyes are definitely clear brown, not hazel or dark green.


The genetic determination of eye colour is more complex that simple medelian heritage.

Vlad Cletus
Saturday, March 27th, 2004, 08:03 PM
Doesn't a Grandparent on each side have to have inherited blue eyes in order for the blue-eyed gene to show up in the random numbered generation offspring?

PeterMW
Saturday, March 27th, 2004, 08:57 PM
The genetic determination of eye colour is more complex that simple medelian heritage.
Clearly, which is what my counter-example was meant to highlight. So what are the genetics of eye colour inheritance ? There must be a geneticist somewhere on Skadi ?

Fred
Saturday, March 27th, 2004, 09:44 PM
Doesn't a Grandparent on each side have to have inherited blue eyes in order for the blue-eyed gene to show up in the random numbered generation offspring?
That's what I wondered with my girlfriend. I have brown eyes, but the majority of my family is blue eyed, especially from my father where there is no one single brown eyed person I know of. My girlfriend has hazel eyes but her family is overwhelmingly blue eyed and she told me that there is 100% chance our children will have brown eyes, since we are both rather dark eyed, but I told her maybe not: is it possible for our children to be blue or green eyed knowing that our family except us are overwhelmingly blue eyed? (we are one of the very few brown/hazel eyed member of our respective family)

PeterMW
Sunday, March 28th, 2004, 12:25 PM
This site has an explanation of the genetic particulars of eye colour determination, but sadly cannot address the issue in myoriginal post.

http://www.seps.org/cvoracle/faq/eyecolor.html

Graeme
Sunday, March 28th, 2004, 01:05 PM
Eye colour is more complex than the site you mentioned and is definitely more complex than the simple dominant/recessive action of genes a la Mendel. The Scandinavians are good at recording inherited characteristics and I vaguely remember that in a study of some thousands of blue eyed couples, their children were mostly blue eyed, but something like 4% had eyes of a different colour. The eye colour was found to be a mixed shade, not dark brown. Some blue eyed people have brown or green spots in their irises, sometimes the area around the pupil is brownish. It is believed that this is the cause of the anomaly of two blue eyed people producing a non blue eyed child. There is also a gender difference in that females are more likely to have brownish eyes than males, their brothers for instance. A blue eyed woman has an equal chance of having a blue eyed brother, but a blue eyed man has only 50% chance of a blue eyed sister.

I presume the child has light brown eyes not dark brown, and its eyes may be mixed brown blue. Seeing a person's eye colour is more difficult than one would think. You have to get very close to the person - it can be rather invasive of personal space. If you come from a mostly blue eyed family and your partner also it is likely that offspring will be mostly blue eyed with some green and brown eyes. It depends on how many children you expect to have. Anyway eye colour does lighten slowly with age. Just having the genes does not mean that they produce a result, it depends on penetrance and expressibility and the effects of other genes.