Making melanin (black) pigment starts with the amino acid tyrosine. It goes through a dozen or so chemical changes before becoming melanin. Tyrosinase is the enzyme that catalyses the first two chemical changes. One gene carries the information for making tyrosinase. If the gene changes enough, the resulting enzyme can't do its job, and no melanin gets made. The changed gene has become a tyrosinase-negative albino mutant gene.
Some animals lack melanin but have normal tyrosinase. Then the mutant gene causing the lack is called the tyrosinase-positive albino mutant gene in spite of having nothing to do with tyrosinase. A better name would be the _____-negative mutant gene, where _____ is filled with the name of the defective enzyme. Unfortunately, we don't know the name of the defective enzyme, yet.
The Dopa Test is a biochemical test that determines whether a mutant gene is tyrosinase-negative or not. Information about it is in H.B. Bechtel's book, Amphibian and Reptile Variants.
Ideally, there is one tyrosinase-negative mutant gene and one tyrosinase-positive mutant gene. Too bad the real world does not conform to that ideal model.
In leopard geckos, there are three unrelated albino mutant genes. Nobody has done the Dopa Test on any of them. Not more than one of them can be the tyrosinase-negative mutant. Possibly none is the tyrosinase-negative mutant.
Albino black rat snakes, corn snakes, and some others have been tested with the Dopa Test. But many others, including albino boa constrictors and ball pythons, have not. In boa constrictors, there are two albino mutants, Kahl albino and Sharp albino. Both are called tyrosinase-negative mutants without any evidence. Only one can be the tyrosinase-negative mutant, but which? And possibly both are tyrosinase positive.
In boa constrictors and some other snakes, any mutant gene that reduces the amount of, but does not eliminate, the black pigment is called a tyrosinase-positive albino mutant gene. This adds several more unrelated mutants to the mixture.
In corn snakes, the amelanistic mutant gene is the tyrosinase-negative mutant. Another version of the gene, ultrahypomelanistic or ultra, is in snakes that can produce some melanin. Work done on the lab mouse indicates that this mutant gene produces a tyrosinase variant that can catalyse some tyrosine. So now we have at least one tyrosinase-positive albino mutant gene that actually does affect the tyrosinase.
Confusing? Absolutely!
Standard operating procedure in mice is to give each mutant gene a unique name and then make groups of the ones with the same location in the chromosomes. For example, in corn snakes, the amelanistic and ultra mutants would be in one group, while the hypomelanistic mutant would be in a group of its own. IMO, herpers should follow this procedure, too.
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