T positive is a name without biochemical significance. It is what people call a couple of mutant genes that lighten a boa constrictor's color. As I understand it, these snakes are roughly halfway (or maybe a bit lighter) in color between normals and albinos. There are probably photos on the web, but I don't have a link off the top of my head. As far as I know, despite having a similar effect, the mutant genes have no biochemical or genetic relationship. Which is why they would be better off with unique names.

Both mutant genes are reputed to be recessive to their normal versions. In other words, to get either one, both parents must have at least one copy of the mutant.

T positive comes from "Tyrosinase positive". Tyrosinase is one of many enzymes required to make melanin (black pigment). Since these "T-positives" have some black pigment, they must have a functional tyrosinase enzyme. Albinos (no black pigment and pink eyes) are believed to lack the tyrosinase enzyme, which is why they are called tyrosinase negative.

Unfortunately, this scheme is too simplistic. Some albinos lack all black pigment because they lack tyrosinase, and other albinos lack all black pigment in spite of having a functional tyrosinase enzyme. Instead, they lack some other enzyme required to make black pigment. Nobody has tested Kahl and Sharp albinos to see which has functional tyrosinase and which lacks it. Maybe both have functional tyrosinase.

Hope this helps.

Paul Hollander

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