Sh is an incompletely dominant gene. What this means is that if it is present it will always be expressed, but it will usually result in more white when an animal is ShSh than if an animal is ShS, ShSp or Shs. A ShSh animal will usually express a white face, white on the legs, belly and often on the nape of the neck (featherneck). Any of the other combos will usually express white on the face, possibly some white on the belly or legs, and usually a small to no featherneck.
Both of these animals exhibit the ShSh pattern.They are both purebred Hereford. Notice however the difference in the amount of white on them.
This animal is also ShSh, Every calf she has produced has either been a white faced or hereford marked animal.
All 3 of the above animals are ShS. They have 1 gene for hereford markings and the other is for solid colored. The amount of white on them varies, but is generally less than the amount on the ShSh animals.
Sp works very similarly to Sh, in addition it is equally dominant to the Sh gene. A SpSp animal will have white along the back, down the hind end and tail and up the belly. The head, sides and legs of the animal will be colored. SpS or Sps animals will be marked similarly, although usually less white will be expressed. Often only the tail and possibly the belly will be colored. SpSh animals will exhibit the white face, often with a stripe down the back and tail, possibly the tail will be white and there may or may not be white on the belly and feet.
I have no pictures of any Sp animals, so if anyone has some, and the background of the animal I would appreciate it.
S is recessive to Sh and Sp but dominant to s. SS animals will be solid colored. They will not have white on them due to any of the above genes. Although there are other genes that can put white onto a SS animal.Ss animals are also solid colored. They again will not have any Sh or Sp characteristics. You have seen the pictures of ShS animals above, here are some of both SS and Ss.
The 2 above animals are SS. They are homozygous for the solid color, and can only pass on the S gene.
Both of these 2 are Ss animals. You cannot tell by looking at them, but they are both out 1 ss parent, and one S parent.
And finally we come down to the s gene. The s is responsible for the recessive spotting gene. Like the red color gene s can hide, you cannot tell by looking at an animal if it is there or not. s is responsible for the spots in the Holstien, Shorthorn, Simmental and many other breeds. A Shs, Sps or Ss animal will only exhibit the characteristics of the dominating gene. The animal may still pass on the s gene, but you will not necessarily see or know this. ss animals are spotted. if an animal is ss it will always be spotted, and can only pass the s gene on. The spots may be large or small. There may be lots of them or almost none of them. The animal can be almost white, or almost solid colored. The Ss animals are pictured above, here are some ss animals.
All of the above animals are ss. As you can see the amount of white that is expressed can be almost none to lots. There are different genes that affect the amount of white expressed.
This animal is in fact Shs. She looks a lot like a hereford marked animal.
It is actually my belief that the s works with Sh, and that it is not completely recessive. We have too many Sh animals that have extra spots on them for me to believe that it is totally recessive to Sh. Of course, it could be a totally different gene that is working here too. All the above spotting/marking genes have other genes that modify them. That is why some animals express more white than other animals do. It is why ShS animals can have extra white, and why ShSh animals can have extra white. Sometimes the only way to know what genes an animal has is to see what is passed on.