Dimples is a dominant gene, yet it is uncommon to find someone with dimples. Why is this the case?

Answer 1

Having dimples is rare because the dimple version of the gene is rare. And as long as there is no advantage or disadvantage to having dimples, then the relative amounts of people with dimples won’t change over time in a stable population.

Let’s go a bit deeper to see what I mean. As you’ve said, dimples are dominant over not having dimples. In genetics, the dimple version of a gene is D and the non-dimpled version is d.

Remember, we have two copies of most of our genes, one from mom and one from dad. You will have dimples if both copies are D (DD) or if only one is D (Dd). That is the definition of dominant.

And of course, if both copies are d (dd), then you don’t have dimples. In our world, most people do not have dimples. There are a few DD and Dd types around, but most everyone is dd.

And it’ll stay this way even though dimples are dominant over not having dimples. Why? Because D is rare. And if there is no advantage, then there is no reason for it to increase in the population.

Answer 2

Muscles smooth over the dimples as one ages.