Tyrosinase is the enzyme that controls rate of the production of melanin – both phaeomelanin and eumelanin. It is actually the same catalyst that causes potatoes to turn black when they are exposed to air after peeling. In mammals, it is involved in melanin synthesis – which affects how much pigment is expressed in the skin. The more tyrosinase, the more pigment.
In Himalayans, the tyrosinase is maximally active at temperatures below normal body temperature and it is actually inhibited at the normal body temperature. This is what makes the Himalayan thermosensitive
In cats, colorpoints (like Himalayans or Siamese) are caused by a partial albino gene on the C locus, much like the Himalayan gene in cavies. However it has a few differences, including the fact that it is actually caused by two different (but similar) alleles on the C locus – cs and cb. When homozygous for cs, you have a mink cat (the darkest of all of the patterns, with only some paling on the abdomen, this can actually look like a self cat). Homozygous cb produces a point cat, what most people think of as a “siamese” cat. When heterozygous cscb, the cat will be burmese, which is between point and mink.
One thing you will immediately notice when comparing any of the above cat colorings with cavies is that first of all, the cats do not have the pink eyes of our cavies and second of all, they lack the white bodies and instead have a gradually fading color that blends from light to dark with no clear distintion like we have in cavies. In fact, if you were to compare to rabbits, cavies resemble the Himalayan or Californian while cats resemble the Sables, Seals, and Siamese colorings.
Genetically, these are more similar as well, and the lettering suggests this, with the Himalayan gene in both rabbits and cavies being noted as ch. Sable, seal, and siamese in rabbits are caused by the Dark Chinchilla gene, a gene that removes all phaeomelanin and removes partial eumelanin – leaving the color on the darker points, but allowing a gradual fading to the lighter areas which still retain color.