I have checked your archives on polygenetics and several
other areas and have not found a concrete answer to this question. Is it
possible to have two parents who have blue eyes have a brown eyed child.
I thought that from the answers given in some of the questions regarding
alleles and genes that it is possible.
I have read that it is possible. With at least four genes and many
different alleles for eye color in humans (plus modifier genes), it can
happen. However, it is extremely unlikely! I have seen green eyes from
brown eyed parents. With the human genome project coming to conclusion,
we'll begin to see these relationships.
Polygenic traits determine the RANGE of a phenotype. ie. there 3 alleles
that determine skin color. So there is a range of dark skin to light skin.
If one person has all dark alleles and marries a person who also has only
dark alleles they will have children with only dark skin. Having blue eyes
is like having light alleles. If two parents have blue alleles, their
children can only have blue eyes. If there are any brown alleles in either
parent, it may be enough to override the blue alleles.
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Update: June 2012