Classic examples of mendelian inheritance are genetic diseases such as sickle-cell anemia, Tay-Sachs, cystic fibrosis, and xeroderma pigmentosa. For some of these diseases, it is believed that they evolved because the genes gave a beneficial effect that outweighed the rare occurrence of the disease (e.g sickle cell and protection against malaria).
However, all of these are examples of uncommon phenotypes, usually less than 1% of the relevant population (where it is most common) has those diseases. I'm interested in examples of mendelian inheritance where variation is common (all of the relevant phenotypes have, say, >5% frequency or something like that).
Consider eye color. In European populations both blue and brown eyes are common phenotypes. Many people have probably experienced a typical high-school class of biology, where this was introduced as an example of mendelian inheritance with brown eyes being dominant and blue eyes being recessive. However, modern studies (for example, genome-wide association studies) show that things like eye, hair and skin color are all polygenic traits. See for example (Sulem, ..., Stefansson, 2007).
Throughout the years I've heard of other traits that some said were examples of mendelian inheritance. Being able to roll the tongue, for example. This question was inspired by this recent question where absence of teeth (Hypodontia) was taught to the OP as an example of a dominant trait. The current answer says that hypodontia is probably an example of a polygenic trait that interacts with certain environmental effects. This got me wondering whether there even are examples of common mendelian variation.
I don't quite know the best way to phrase it, but my question is the following:
Are there any examples of human phenotypes that are due to mendelian inheritance where all of the phenotypes are common?
Take eye color as an example again. By common, I mean that both blue eyes and brown eyes are common (over, say, 5% in for example Sweden). On the other hand, for example Tay-Sachs disease occurs only about 1 in 3,500 among Ashkenazi Jews where it is most common, according to Wikipedia. Way less than even 1%.
Preferably I want it to be verified by modern genomic studies (such as GWAS) that it is an example of mendelian inheritance. If such an example does not exist, then I will accept any answer that provides modern, relevant scientific literature that explores this topic. For example, it might explain why we would not expect to see common variation due to mendelian inheritance.