MadSci Network: Genetics

Re: Can hazel and green eyes produce a child with brown eyes?

Date: Wed Sep 6 15:54:38 2000
Posted By: Christopher Carlson, Ph.D.
Area of science: Genetics
ID: 967041105.Ge

Wow.  Scientifically your question is straightforward, but the ethical 
implications are pretty serious.  Honestly, your friend really ought to know 
who daddy is, but you didn't ask me to pass judgement so I won't.

In high school biology we are taught that dark hair, skin and eye color are 
dominant over light, as an example of how the concepts of Mendelian genetics 
are applicable to humans.  Unfortunately, this is a serious 
oversimplification of the genetics of pigmentation.  There are urban legends 
that this has led to some pretty serious heartache over the years, when 
children with dark eyes/hair and light eyed/haired parents come to the 
conclusion that they must be adopted, and their parents never told them.  
This is not necessarily the case: it is definitely possible for two light 
eyed/haired parents to give birth to a child with dark eyes/hair.

In fact, there are many different genes which contribute to the pigmentation 
pathway in humans, with the result that there are no discrete colors of eye 
in human, just a spectrum of colors between green, blue, hazel, and brown.  
For that matter, the iris in a single person has many different colors in 
it, if you look closely enough.  All of these color shades are the end 
result of the production of two pigments, one yellow and one black.  In the 
absence of either pigment, the iris appears blue.  Increasing doses of the 
yellow pigment result in a variety of shades between blue and hazel, 
including green.  Increasing levels of the black pigment darken the iris to 

There are a number of genes in the pathways leading to production of each 
pigment, and the overall levels of activity of these genes will determine 
the level of pigmentation in the iris, and thus eye color.  Because there 
are so many genes contributing to pigment production, it is not really 
possible to predict the eye color of a child given the eye color of the 

So the short answer to your question is that eye color is not a reliable way 
to predict the father of the child.  Given light eyes in the mother and dark 
eyes in the kid, if one of the candidates had dark eyes, I'd say he was more 
likely to be the father but even then paternity would be far from proven.  
Blood tests could probably rule one of them out, but I get the sense that 
your friend doesn't want the guys to know she's unsure.



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