1 Brown/1 Blue eye

[Keith Robison]

John Bohmfalk (bohmfalk at tcgcs.com) wrote:
: I have a student who has one beautiful brown eye, and one beautiful blue
: eye.  Do any of you know the genetic/molecular mechanism behind this
: phenomenon?  Any idea how common it is?  I would appreciate any
: information, or references.

Presumably your student is exhibiting genetic mosaicism.  Blue/brown
eye color is autosomal, so we can rule out the trivial explanation
that your student is female & we are observing X-inactivation.
That leaves a couple of hypotheses, probably none easily testable
(though a clever PCR experiment might do the trick -- hmm, perhaps
getting samples via an eyewash).  One possiblity is that the
brown allele was inactivated by a somatic mutation; the other is
loss of the brown allele via somatic recombination (I haven't 
a clue as to which has a higher frequency).

You might look in OMIM for more background on the genetics of blue
vs brown.

Anyway, a good genetics textbook should cover these topics
(the current edition of Griffiths et al, An Introduction to
Genetic Analysis is excellent, with very good choices of
photos to illustrate points such as these).

Good luck!

Keith Robison
Harvard University
Department of Cellular and Developmental Biology
Department of Genetics / HHMI

robison at mito.harvard.edu