Human eye color genetics

Bert Gold bgold at
Wed Jan 17 18:18:10 EST 1996

In the 3rd edition of Curt Stern's Principles of Human Genetics
(WH Freeman: San Francisco, 1973) at page 78, near the bottom,
Dr. Stern tells us:

An oft quoted example of dominance in two alleles which both act
on a normal trait is that of brown and blue eye color.  It is usually
stated that there is a pair of alleles, B and b, that control eye color, 
and that BB and Bb produce brown eyes, and bb blue.  This description
is only an approximation of the truth.  The irises of some blue-eyed
persons contain small spots of brown pigment which may not be noticeable
without careful inspection.  Two such seemingly blue-eyed individuals
can have brown-eyed children.  The genetics of eye color is complex
and not yet fully understood.

Then, at page 574, Dr. Stern informs us:

... Some mosaic human abnormalities have been suspected of being
due to mutation during early embryonic development, but there is
no definite proof of this.  The later in development mutation occurs,
the smaller should be the segment of tissue derived from the mutant cell.
Thus, some of the fairly common mosaic eye colors -- a brown segment
in an otherwise blue iris, for instance -- are perhaps due to late somatic
mutation.  Similarly, retinoblastoma in individuals whose parents and 
offspring do not have it may be caused by somatic mutations.

P.S.  Sometime, check out David Bowie's eyes:  They are absolutely

Bert Gold, Ph.D.
University of California, San Francisco
School of Medicine
Program in Medical Genetics

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