Quite some time ago (like, well over a year), I acquired Irwin, a male Kenyan sand boa who has become a favorite amongst people quite rapidly (even if he is a headache for me at times, what with snubbing his food for no good reason). When the opportunity arose though, I couldn't say no to getting him a future girlfriend, and one that is very, very different from him. Irwin is a standard, wild-type boa in color and pattern, but Marmora (whose name means "marble" in Greek) is anything but.
And this is where I make a disclaimer: some people, for whatever reason, absolutely hate morphs, mutations, etc. in reptiles, and think the standard wild-type variations should be the only ones kept. I, personally, have to throw that notion out the window; while I love the common wild appearances of most species, the morphs that captive breeding capitalizes on so often not only are also occasionally found in the wild (and are rare due more to the numbers game that statistics for homozygous recessive animals are than any real deleterious impact in the vast majority of cases), but of course once in captivity are no longer under pressure to survive in the wild environment and do perfectly fine (again, for most; a rare handful of mutations have deleterious issues attached, not including problems from inbreeding which is an entirely separate issue any breeder should try to avoid). Under our care, they provide a fantastic first look as well into the effects of genetics, point mutations and polymorphisms or line-breeding (artificial selection), and other subjects.
The traits Marmora possesses are no exception. She is a double homozygous recessive animal, meaning she carries two copies each of two different recessive genes, which each have an interesting effect on color alone and together produce a third appearance altogether unique.
Many animal species possess a mutation (sometimes multiple) that result in a lack of black or brown pigmentation produced by melanin; in mammals, where melanin is often the only pigment producing color, this is referred to as albinism. In many birds, most reptiles, amphibians, and fish etc. however, which have multiple color pigments, true albinism is rare and the singular lack of melanin is simply referred to as amelanism (or should be; a lot of people still erroneously call amelanistics "albinos"). In sand boas, this results in a yellow-orange snake with white, tannish, or purplish blotches. Their eyes also lose much of the pigment and instead show up as ruby red from the blood vessels in the pupil, and grayish or bluish from the muscles in the iris.
Another common mutation in animals with many pigments is a lack of red/orange, or yellow/orange pigments, the former being anerythrism and the latter axanthism. In sand boas, I believe the pigment giving their sandy orange colors is xanthin rather than erythrin, so their common mutation would be an axanthic, a snake with a white background but black blotches. When you cross an amelanistic animal with an axanthic, you get...a bunch of normal, wild-type animals.
Why? The two mutations are located in entirely different genes, in entirely different regions of their genome. One snake with one recessive mutation still has the normal gene for the other, so when you cross them you get babies that have dominant, wild-type gene for both traits, but are heterozygous, or carriers, for both of the recessive traits. When you cross this second generation together though, you get a one in four chance of a baby getting the recessive trait for each gene, from both parents, creating a double homzygous-recessive animal lacking both xanthin and melanin and presenting as a white-and-tan, pigmentless (more or less) snake: a snow sand boa, something that just might qualify as a true albino.
But, there's one more wrench the sand boa throws into the mix, and you've probably noticed it in these images of Marmora: she's a snow, but oddly enough, she's not lacking ALL of her black pigment. Why? Because she has a variation of the amelanistic mutation known as "paradox amelanism."
The standard amelanistic gene, lacking all the black, isn't even originally a Kenyan sand boa trait. A different species, the Egyptian sand boa, was bred into the Kenyans in order to pass on the amelanistic trait into them so as to make amels, and snows; all snakes with this "pure amel" trait then are not pure Kenyans anymore, at least not entirely (after several dozen generations of outcrossing the contamination from the other species becomes rather minimal). But a few decades ago (in 1995 to be exact, so as long ago as I've been around), a unique, pure Gongylophis colubrinus (that's Kenyan sand boa by their scientific title) was brought out of east Africa sporting a mutation very similar to standard amelanism, but with one big difference: it also showed several black splotches in the areas where the dark pattern normally was, something amelanism usually gets rid of entirely. Because this pigment reappeared in some places (and it often grows more prominent as an animal ages), it was dubbed "paradox."
The paradox gene behaves just like the regular amel gene, a recessive trait that when paired with axanthism can produce snows. But, they're snows that develop little black patches, looking like spattered marble. Even more interestingly though, if you cross a paradox animal to one carrying the other amelanistic mutation, you'll get...wild-type animals again. The two mutations both cause a lack of melanin, but occur in different loci (places in the genome) so they aren't compatible, and the normal gene from one parent will overshadow the recessive from the other. If an animal comes to possess a double-recessive state for both genes, I suspect the standard amelanism will also overshadow the paradox version as it wipes out all the pigment that the paradox might let bleed through.
Thus, it will become an interesting experiment once Irwin and Marmora both mature and I attempt breeding one day; Marmora, obviously, has recessive genes shining brightly in her. Irwin, he's got nothing as far as I know. Because he only shows the dominant wild-type appearance, he could just be normal, or he could be a heterozygote, carrying recessive genes hidden under the dominant ones. If so, they could pair up with Marmora's recessive traits, and the babies will show up both wild-type and some with the mutations they inherited. If all of them turn out wild-type, then I know they're double hets for two traits, since Marmora can only pass on the recessive genes.
Either way, they'll be adorable...
