How does eye color work genetically?

Patient

Q: How does eye color work genetically? I was under the impression a child could only get the eye color of one of their parents, so I'm very curious how it works. My mother has brown eyes and my father has green. My sister has brown eyes and I have green but somehow my brother has blue eyes. His wife also has blue eyes and they have four children all with blue eyes. How could my brother possibly have blue eyes and carry such a strong gene for blue eyes when neither of my parents have blue eyes?? I'm very confused. (There's no category for genetics so I had to put it in general)

Symptoms:  Confusion
Doctor

A:   Thank you for your question. Eye colour is determined by genetic inheritance from both parents. Now the percentage at which different eye colours will present in directly related siblings will vary depending on the parents eye colours. Unlike other inherited traits, eye colour is determined by a multiple set of genes, therefore there could be many variations that can be passed on from one generation to another. The concentration of a pigment, melanin is what determines eye colour. The more melanin, the darker the eyes. If either parent has different eye colour, then there will be a greater range of eye colour inherited in their offspring, just in your siblings. Your brother's blue eyes is one such example of the genetic variability in eye colour among siblings.

Thank you for consulting AskTheDoctor.com

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