Base Genetic Mutations
Base genetic mutations are single traits, inherited in typical Mendelian recessive fashion. All base genetic mutations in reptiles (that we know of so far) are inherited this way. While most are typical recessive mutations, a few are incomplete dominant, and a few more are suspected to be . To learn more about co-dominance, you may wish to visit our 'Genetics 301 Page'
There are three types of color related chromatophores present in reptiles, each can be modified in one of three ways; a total lack of function, reduced function, or increased function. These three traits are respectively referred to as a-, hypo-, and hyper-.
Traits which affect the melanophores:
This is one of the simplest mutations. These animals are unable to produce tyrosinase. Therefore, no melanin is deposited in the melanophores. The result is a total lack of black and dark brown pigment. To learn more about the two types of albinos (T+ and T-), visit our 'Chromatophores' page and see the section on melanophores.
This trait is actually quite similar to amelanism. Tyrosinase is produced but is blocked from gaining access into the melanophores. Therefore, the amounts of melanin produced are substantially reduced. Often areas which would normally appear solid black are almost transparent, perhaps translucent would be more accurate). Additionally. many specimens seem to have reduced amounts of melanophores present. This may simply be the result of selection for the brighter coloration in captive populations. It is likely that several different alleles may be at work here, all lumped under the term hypomelanism by herpetoculturists.
Frequently shortened to 'Melanism'. This trait, the exact opposite of amelanism, is also rather simple to understand. These animals possess extensive quantities of dermal melanophores. The result is a pattern near totally obscured by black and dark brown pigment. Hypermelanism occurs with some frequency in wild populations. In certain species, this has proven to be something of a survival advantage - and 'melanistic' individuals may comprise a major portion of the population!
Traits which affect the xanthophores:
The reader is advised to remember that any trait affecting the xanthophores may also affect the erythrophores and vice versa, since the two are interrelated.
This genetic mutation slightly more difficult to comprehend. Red and yellow pigmentation is not synthesized by xanthophores. There is no red or yellow pigmentation present in these animals at all. Axanthic animals typically appear as black and white, with intermediate shades of gray.
However, in some axanthic specimens, yellow pigments in the form of carotenoids may be retained in the xanthophores. Additionally, certain iridophores may reflect light in such a manner as to appear yellow. Ordinarily, the iridophores are located in the same areas as the melanophores and are masked by the presence of the black pigment. This condition may cause dark areas to appear brownish, rather than a pure black. It is certain that multiple alleles are at work here, each uniquely influencing the appearance of the specimens involved.
Yellow pigmentation is greatly reduced in the xanthophores. However, yellow pigments in the form of carotenoids may still be retained in the xanthophores. This accumulates with age and may be a major contributing factor in the overall appearance of some animals. It would be expected that red pigmentation would also be reduced in these animals. There are most likely several morphs of captive reptiles which are hypoxanthic masquerading around under other 'genetic labels'. Few herpetoculturists have access to the technology required to ascertain the exact nature of the mutations in today's collections. Fewer still would be willing to sacrifice specimens for examination! Myself included!
Hyperxanthic animals develop intense amounts of yellow pigmentation as they grow, most likely as the result of extreme carotenoid retention. Occasionally, the extreme yellow coloration may be accentuated into an orange coloration where none would normally be present.
Additionally, they seem to have reduced amounts of red pigmentation present. This would most likely be malfunctioning of erythrophores, and perhaps this mutation would more properly be called anerythrism. Unfortunately, this term has already been applied to another mutation (see Anerythrism 'Type A'). Perhaps much of the confusion surrounding cornsnake genetics is simply the result of inappropriate naming of the earliest mutations, leading to confusion over the mechanics involved.
Traits which affect the erythrophores:
Red pigmentation is not synthesized by xanthophores. Yellow pigmentation in the xanthophores is still present. Additionally, yellow pigments in the form of carotenoids are still retained in the xanthophores. This accumulates with age and may be a major contributing factor in the overall appearance of some animals. Typically, anerythristic reptiles appear as black and white animals, with varying amounts of yellow present.
Red pigmentation is greatly reduced in the xanthophores. Yellow pigmentation in the xanthophores is still present. Additionally, yellow pigments in the form of carotenoids are still retained in the xanthophores. This accumulates with age and may be a major contributing factor in the overall appearance of some animals.
The exact opposite of anerythrism, this trait causes excessive amounts of erythrophores to be present and enabled. The result is an animal with extensive red pigmentation.
Traits which affect all chromatophores:
Leucistic reptiles are completely lacking in all pigmentation and usually appear completely white. Older individuals often develop dark smudgy coloration, possibly through the same process which adds dark pigmentation to tyrosinase positive albinos. (To learn more about T+ albinos, visit our 'Chromatophores' page' and see the section on melanophores)
Oddly, all known leucistic reptiles possess either normally pigmented eyes or solid black eyes. These dark eyes provide a startling contrast. It has been proven in the Texas Ratsnake (Elaphe obsoleta lindheimeri) that these dark eyes can be 'removed' by out-crossing the leucistic mutation to an amelanistic.
Calico animals develop varying amounts of white scattered patches, usually during later years of life, although some appear calico at birth. The spots are usually small, appearing as freckles which may form into larger blotches. Often the white is concentrated in areas where white pigmentation normally appears, such as around edges of markings.
Piebaldism gives the appearance of large scattered solid white patches. Generally the normal patterning adjacent to the white areas appears 'bent' or 'melted'. Often this mutation manifests itself as a single large white blotch located on a posterior flank. In other specimens, a nearly complete ring of white appears in roughly the same locality. The most extreme individuals are nearly totally white, with normal patterning appearing only on the head and tail.