Okay, this is my understanding, though I have not tried to explain it in a while, and a person more well-informed than myself will probably correct me in several ways very soon. Ever notice the plus sign doesn't show up at these forums? It gets parsed as code, and so we don't see it, I guess.
T , T-plus, or T-positive means Tyrosinase positive. Tyrosinase, if I remmeber correctly, is an enzyme which allows melanin to bind to the melanophore, so that you and I can see the lovely black overwash on our prize "het". Normally, "Albinos" (amelanistic) do not produce Tyrosinase, which is what facilitates the failure of the melanin to bind to the cell. (Again, please, this is my best understanding of it. Go ahead and correct, but don't flame, k?)
In what we call "T-Pos Albino," animals, apparently the Tysosinase remains, and yet the Melanin still fails to bind correctly, actual possible reasons for which are as mysterious as they are multitudinous.
It is really not known exactly how Tyrosinase does its job, nor have we confirmed, in many cases, that what we are calling "T-positive" animals, actually are producing Tyrosinase. This sort of testing is very expensive, and if it makes a purple and orange snake, that's good enough for me. (have you seen the Clumper Strain T-positive Pituophis catenifer annectans? WOW)
As far as whether the term is appropriate for common usage; Well, I would say there are more misleading names out there, and this one will do for now. Though technically it may be considered more closely akin to what we currently call "hypomelanism," than true amelanism, it is misleading to use the term "T-plus Hypo," as well.
Hypomelanism is surely arrived at by different mechanisms both within species and across species. I believe there are now 5 different kinds of identified, genetically heritable hypomelanism mutations in Corn Snakes. One of these is an allele to common amelanism within that species. (if you want to stretch your brain, go learn about how alleles work, they are different mutations on the same gene pair.) I believe that it would take an especially naive individual to think that what we call "Hypo" in Boa constrictor is the same as that which we call "hypo" in any other species, and vice- in- ex- intra- infra- ultra- and contra- versa. Similarly for "T positive" critters, it is an unknown function for now.
Most of the actual molecular genetic complexities, specifics, and causal relationships of color and pattern mutation and variation are unknown, and will remain unknown for quite some time, I'd guess. The world isn't really interested in the "pretty" genes of our snakes, so we'll have to wait until Apple releases "iGenome."
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Jeremy J. Anderson
Gem State Reptiles
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