|MadSci Network: Genetics|
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 brown. 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 parents. 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. Chris email@example.com
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