Double... or is it Triple?

I've always knew that I do not have single eyelids, and have in mind that I have double eyelids. However, I've made a new discovery.

Not long ago, I was curious to find out if my parents had single or double eyelids. I observed their eyelids and found out that they both had double eyelids. Strangely, I noticed their eyelids had only one extra fold of skin. I recalled that I had two extra folds of skin on my eyelids when I last examined them.

In order to clear my doubts, I examined my eyelids once more. True enough, there are two extra folds of skin. Now, my question is "Do I have double eyelids, or is mine a (unique) triple?" It may be a product of the genes from both of my parents. My formula: Double1 + Double2 = Triple1.

Double or triple, it doesn't really matter, but that discovery "inspired" me to make further investigations on genes.