Embracing the idea that every tabby cat’s appearance is a result of coloration, the cascade of ASIP, Tabby, Color, and genetic expressions helps cat colors and patterns make a lot more sense.
The scientific community finds more variation in ASIP among domestic cats whenever a deeper exploration occurs. A, A2, a, Apb, AJc, ALs are now identified and very likely there will be additional identifications as more investigation occurs. How these alternate ASIPs affect pattern, color and coloration is yet to be fully understood and the cat enthusiast community will be key to developing that understanding.
ASIP or Agouti Signal Protein determines the frequency of alternating between eumelanin/black based pigment and pheomelanin/yellow based pigment on an individual hair and in areas of the body, such as the face, skull, spine, and tail during the period when the hair is forming. All domestic cats have the same variant of agouti written as “A” sometimes noted as wild type because it is the natural, common form in the species. The previously only variant or mutation in domestic cats noted as “a”, prevents the genetic signals to produce the yellow pigment causing the cat to be “solid” or melanistic.
The variation in ASIP appears to arise from geographic separations in populations as well as interspecific hybridization, with each species seeming to have one or more ASIPs or signals instructing pigment on where and how to move in the cat. The Norwegian Forest Cat is an especially interesting case as the interaction between ASIP and the Amber MC1R variant creates cats that become less solid with age, at several points in their development mirror the appearance of charcoal Bengal cats.
