Eye color question

[KimNu]

Hi all,

First post on this great forum. I'm a beginner biology student, so I have alot to learn. Here's a question I'm having a hard time with:

Two green-eyed parents have a son with brown eyes. Everyone thinks their son is adopted. Explain, with possible genotypes, how it is possible that his parents are his biological parents.

Any suggestions on how to go about this problem? Thanks,

Kim

[MrMistery]

This might be a trick question. From what I know eye color genetic determination is not known...

[bekarzi]

I don't know for sure, but...
Brown is a dominant eye colour to my knowledge, thus it's more common to be passed on through genes. Perhaps the two green eyed parents both come from a family of predominantly brown eyed people, and so passed a gene onto their child that way? Like, if you have
("Dad" and "Mum" here would be the grandparents of the child, and the only green eyed children they have would be the child in questions parents, and then to the far right is the child...)

DAD --- MUM
Gr | Br
___________|______
| | |
Br Br Gr _________
|
DAD --- MUM |
Bl | Br |________Br
______|______ |
| | |
Br Gr _________|

Like the genes for brown eyes are carried by the parents but not "possessed"... If that makes sense? A recessive gene is the term I think...

I'm not sure cause I'm just a year 11 bio student, but thats the only reasoning I can create. I hope it was more help than hinderance or confusion!

[bekarzi]

dammit the thing removed my spaces....

anyway, this is kind of what I meant
http://www.biology-online.org/2/4_crossing_over.htm

If you type "Genotype" into the bio-online search engine some information should come up

[MrMistery]

Even by your reasoning that could not happen: if brown is dominant then both parents need to have no brown alleles(they have to be homozygous recessive), which means all their children would also have brown eyes. But eye color is not a monogenic trait. From what I know, at least three separate loci have been discovered that contribute to the trait of eye color.

[KimNu]

Hey everyone, thanks for the responses. I've been confused by this issue, but I did a little more digging and it does appear that two greenish eyed parents can produce a brownish eyed kid. See here:

http://www.sandwalk.blogspot.com/2007/0 ... color.html

Thanks,

Kim

[Darby]

There are LOTS of eye color alleles, including dark green alleles and light brown alleles that can be hidden by them - if each parent worked that way, and the child had 2 brown alleles, that would work...