Polygenic traits are exactly what the name implies, traits controlled by multiple alleles. One good example is that hair color and skin pigment can be polygenic. The ratios of polygenic traits tend to follow a bell curve. Many times polygenic inheritances are mistaken for simple cases of dominant-recessive Mendelian inheritance. One example of this is the trait of tongue curling, which was first thought to be dominant, but that has been proven wrong, and it is now thought to be polygenic.