genetically it is impossible for two brown eyed parents to have a blue eyed child
Someone on yahoo answers asked a question, why they had blue eyes whilst both their parents had brown eyes, the answer:
It is because brown eyes are dominant that they can hide for generations. Here's a quick explanation.
You inherit two genes for each trait, one from each parent. But in order for you to have brown eyes, you only have to inherit a brown gene from one parent. The other gene can be blue - but it will be overridden by the brown gene. If you then have children with a person who also has one brown gene and one blue gene, the child has a 25% chance of inheriting two blue genes and will therefore have blue eyes.
If B represents a Brown gene, and b represents a blue gene, the family tree looks like this:
Mother - Bb - brown eyes
Father - bB - brown eyes
Child can be any one of these:
Bb - brown eyes
BB - brown eyes
bB - brown eyes
bb - blue eyes
So 1 in 4 chance