Black Unders genes all attach to the same area, creating a series. Creatures can only have two genes in a series at most, one inherited from each parent.
So they could, for example, be MaD (or) MaMa (but not) MaMa/D. They could also be nn for the series, and have no markings here.
Black Unders Series genes are codominant, meaning having more than one different type will show the effects of both.
However, having duplicates, like two copies of Ma, will not create two different types of Mask.
Black based, affected by any genes that target black such as merle
Short black stripes going horizontally down the bottom of the face, neck, belly, and/or tail. Can also affect insides of legs down to the feet.
Usually both sides are the same, and stripes are thickest in the center and narrower along the edges, but atypical patterns can occur
Can affect all zones or only some of them
Can be very dense or very sparse, but will retain a stripe-like pattern
Can fade slightly toward the edges
Skin is not affected. Eyes are not affected.
In hooved creatures, tail is black where stripes are present