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Both W20 and Frame (Olw) are modifier genes. Without a pattern to work on, or with a pattern they cannot significantly modify like roan, they may be silent or very minimally expressed. But with a pattern they can modify, they can significantly change that pattern.

Frame modifies the way patterns like Splash and some White Spottings are expressed by pushing the color to the edges of the body, "framing" the white patches. It may also give jigsaw type edges to the white patches.

W20 seems in increase the amount of white marking within the parameters of the white factor involved. It is more expressed with certain genes (like W10) even with low white factor.

Eventually Ammit is working on removing the lethal interactions of specific Kit genes (frame will always be homozygous lethal as it is in real life) to replace it with an algorithm for foals with excessive white markings being lethal. This would mean you would be looking at a breeding situation that more accurately reflects real life. We aren't quite sure how this will work yet but when it comes in it will make breeding KP horses way more fun because you could combine patterns that are currently lethal together.