David's Eye Color Situation

This week's episode introduced us to Jack's diagonal son, David...and his beautiful blue eyes. Many have wondered aloud if David's blue eyes suggest that (since Jack has brown eyes) his mother is necessarily blue-eyed. I have replied, sometimes a little too hastily, that genetically, the mother could have brown or blue eyes.* What I also realize is that Lost is exactly the type of show that would cast a blue-eyed child actor just to hint strongly at the identity of Jack's diagonal ex-wife. It's probs Juliet.

*Below we see a Punnett square. Since I have tried three times to explain this simply to no avail, I will guide you to the correct section on wikipedia's "Genetics" page. Please skip down to "Discrete Inheritance and Mendel's Laws." Basically this little section explains how for every gene (eye color, for instance) your parents each donate an allele. Two alleles determine how that gene is expressed. Alleles can be dominant or recessive. If just one of the alleles donated by the parents is dominant, the dominant trait will be expressed (in our case, Brown eyes are dominant. Even if a mom passes down a recessive blue-eyed allele, if dad passed down a dominant brown-eyed allele, the kid will have brown eyes). Two blue-eyed parents must both have all recessive alleles, thus they can only pass down recessive alleles; thus two blue-eyed parents must produce blue-eyed offspring (see: me). However! Since it only takes one dominant allele to express brown eyes, we never know for sure if brown-eyed people have the genotype Bb or BB. At this point we become genetic detectives and I'm still not so sure I did a good job explaining all this.

Now! Two brown eyed parents could both have genotype Bb. Since they each have a dominant allele, they have brown eyes. But when they reproduce, they might pass down their alleles in such a way (pretend the As are Bs): which means that there's a 25% chance that the child of two brown-eyed people (with genotype Bb) will have blue eyes, since there's a 25% chance he'll get two recessive genes.

Thus, Jack could have genotype Bb (he must, actually, because his blue-eyed father Christian HAD to pass down only recessive alleles), and his lovely ex-bride could, too. So David could have a brown-eyed mom, but let's face it, they did it for a reason.

PS I started this post last week, then spent the last three days (and today) sick as a dog (Vincent), so even though I wanted this to make sense, it still might not.

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