Ask A Scientist Molecular Biology Archive

name         Nick M.
status       educator
age          50s

Question -        I have one biology student that has one blue eye 
and one brown or green (cannot remember which it is).  How is this 
possible with all DNA carrying the same information?
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Eye color is actually coded for by more than one gene.  The process of eye
color development entails a step by step process and is separate for each
eye.  It may be that one eye doesn't complete the whole process and stops one
step short of full eye color development.

vanhoeck
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I have seen this in two people...I am not sure but here are some
possibilities.  First off, eye color is NOT as simple as the text books
would have us believe.  There are more than three genes involved.  At least
one for pigmentation and one for the thickness of the iris. Green is a
transition I believe between blue and green.  If one has a thicker iris and
what might typically give pigmentation of blue one gets green .  If the same
amount of pigment is in a  thin iris it results in blue.  It is also quite
possible that the genes are the same for both eyes but because of some
developmental anomaly the lighter eye has had its ability to generate
pigment interrupted.

Peter Faletra Ph.D.
Assistant Director
Science Education
Office of Science
Department of Energy
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