So my friend is one of five children. Her parents both have brown eyes and so do all of her siblings but her eyes are blue? She's wondering how is this possible?
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It's possible for her to have blue eyes because both of her parents have brown eyes but can still carry the gene for blue eyes. For this to happen, both parents must be carriers of blue eyes, while still having brown eyes. This would also explain why 4 out of 5 children have brown eyes, because brown eyes are a dominant (common) trait and when both parents have the same eye color, their offspring are very likely to have the same eyes.
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Brown eyes are a dominant trait. Each person has a set of genes from each parent. If you get one blue and one brown, your eyes will be brown. If both parents have one brown and one blue gene their child could have blue eyes if she gets a blue gene from each parent. If both parents have blue eyes that means both have 2 genes for blue eyes, they will both have blue eyes and their child cannot have brown eyes.
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Her grandparents might have blue eyes?