Big B, little b

Now that I've made an effort to combat the bandying about of the term projectile vomiting, it's time to address another popular medical misconception.

My kids' brown eyes frequently elicit comments, which often include the observation, "Because even though you and Pete have brown eyes, your kids could still have blue eyes." Then follows a reference to big B, little b and recessive and dominant genes. And the concluding statement is invariably: "But parents with blue eyes can't have brown-eyed kids."

Even the Eye Color Calculator refuses to give me results for my children, stating that I cannot be the child of my parents:

I hate to break it to you, but when your high school biology teacher made that Punnett square explaining the transmission of eye colour, he was dumbing things down. Simple Mendelian genetics applies to the colouring of corn kernels and the shape of peas. Human iris colour is more complicated.

Eye colour inheritance is multifactorial. Several genes are involved, and the occurrence of mutations further complicates the possibilities. Though uncommon, blue-eyed parents can have brown-eyed children.

So that Dutch cousin of yours with the brown eyes, whose paternity you've always secretly questioned? Probably legitimate. The cousin, that is; not your suspicions.