MadSci Network: Genetics |

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Hi Angie, Eye color is not nearly as simple as you may have been led to believe, because there are truly infinite gradations across the spectrum from blue to green to grey to amber to brown. However, for the sake of argument, let's assume that there are only two colors: dark and light. Furthermore, let's assume that these two eye colors are the result of genotype at a single locus with two alleles: B (dark) and b (light), with B dominant over b. Humans are diploid, receiving one copy of the genome from each parent, so individuals with genotype bb will have light eyes, and individuals with genotype Bb or BB will have dark eyes. You and your husband are both dark eyed, and therefore either Bb or BB genotype. So, in this simple model, the probability that you and your husband (both dark eyed) would have a light eyed child is the product of the probability that you are both genotype Bb and the probability that the child inherits the b allele from both of you. If we knew that you both were Bb, then the probability of a bb child would be 25%. However, working out the probability that you and your husband are both Bb is considerably more complicated, and not really worth the effort given that we know our model is oversimplified to begin with. Suffice it to say that the maximum probability of a light eyed child under this simple model is 25%, but we made a number of assumptions (how many genes are involved, what the dominance relationship between alleles is, etc.) and therefore this number is only academically accurate. From a more realistic prespective, the answer I'd have to give is that it is certainly possible that you and your husband could have a light eyed child, but it's more likely that the child's eyes will be in the same range of the spectrum as you and your husband. I honestly can't give you a more accurate prediction, because scientists have only begun to scratch the surface of pigmentation genetics. If you are interested in more detail, please read my previous posts on this topic in the archives. Chris Chris

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