Re: What combinations of eye color can hazel-eyed people create?

Dear Shannon,

This is a much discussed topic in the MadSci Genetics Archives. Brian Foley cites a nice collection of online resources on this subject in his answer to a question about The Most Common & Least Common Eye Colors for Humans from 5/14/03. As explained in his 1st link to The Genetics of Human Eye Color from Oregon St. Univ., eye color was once thought to be inherited through a single pair, bey2. But it is now believed to be more genetically complex, involving @ least 2 more gene pairs, gey & bey1. Nevertheless, most current genetic models for its inheritance still focus on the bey2 & gey gene pairs, despite the known limitation that "This model explains the inheritance of blue, brown and green eyes but cannot account for gray, hazel or multiple shades of brown, blue, green and gray eyes", as noted in The Genetics of Human Eye Color.

However, hazel eye color is probably most similar to green genetically. If we assume that they are comparable for the sake of argument, we can use some of the established patterns of bey2/gey inheritance to predict your offspring's eye color using the info. on the Phenotypes and Genotypes for Human Eye Colors webpage from the Athro Ltd. educational website on Inheriting Eye Color, cited by Brian Foley. In order for you & your husband to have green/hazel eyes, you both would have to be homozygous (2 copies ea.) for the blue allele of the bey2 gene. While the 2 of you could be either homozygous (2 copies ea. of the green allele) or heterozygous (1 copy of the blue & 1 copy of the green allele ea.) for the gey gene, the fact that you already have children with blue eyes indicates that you would both have to be heterozygous for this gene to be capable of producing blue-eyed offspring, which need to have 2 copies of the blue gey allelle (i.e. homozygous). If this is too confusing, you can try using the Example Crosses from the Phenotypes and Genotypes for Human Eye Colors webpage to sort it out, although they don't specifically show any crosses between 2 green-eyed parents, unfortunately. But based on this model, your offspring should have a 1/4 chance for blue eyes & a 3/4 chance for green/hazel eyes. So obviously your 3/3 with blue eyes would appear to defy those odds, supporting the argument that green & hazel eyes are not equivalent & that other genes are likely to be involved. In addition, I can also tell you that my wife & I both actually have green eyes, & we have 2 children with the bluest of blue eyes as well, so this genetic model might not even hold up very well for green eyes, either.

In conclusion, while it is usually possible, & often most likely, for parents with apparently identical phenotypic traits, such as eye color, to pass those traits along to their offspring, the complexity of multigenetic traits, such as this, can cause the pattern of inheritance to be less predictable. I believe that part of the problem lies in the fact that eye colors such as "hazel", "green", & "gray", are really not specific colors in themselves, but result from a combination of shading patterns regulated by several genes, possibly in a manner similar to that of hair coloration, as described in the Hair Color section of the Genotype -> Phenotype Classroom Booklet from The Woodrow Wilson Biology Inst. So, I would expect that it would most likely be possible for you & your husband, as well as my wife & I, to produce offspring with hazel or green eyes, respectively, but the odds of that occurring are simply not accurately predictable, given the current state of our knowledge.

Thanks for the great question & I hope that this explanation wasn't too confusing,

Jeff Buzby, Ph.D.
CHOC Research Institute
MadSci Genetics Network