Tyrosinase does not produce melanin. Tyrosinase catalyses two steps in the biochemical assembly line that produces melanin. There are a variety of other enzymes that catalyse other steps in the melanin biochemical assembly line. A defect in any of these enzymes could produce a T-positive albino. A genetic defect that changes the shape, size, or distribution of the pigment cells or the pigment granules inside the pigment cell can also produce a T-positive albino.

In T-negative albinos, the black areas are typically white. In T-positive albinos, the black areas can be almost any shade that is lighter than black, including white.

Anything lighter than normal that isn't tyrosinase negative could be called a tyrosinase-positive albino. And there are dozens of ways to make an animal lighter than normal, including a partly functional (rather than nonfunctional or fully functional) tyrosinase enzyme. The coloration of a Siamese cat is caused by such a partly functional tyrosinase enzyme.

As there are no *proven* tyrosinase negative boa constrictors, all boa constrictors that are lighter than normal could be called tyrosinase positive albinos. There are dozens of different ways to make a "T-positive" albino. Which, in my opinion, makes the term useless as a category. It could still be used as the unique name of a single mutant gene, of course.

Paul Hollander

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