Normal

By definition, a “wild-type” has the dominant genes at all of these loci. In other words, a “wild type” has NO recessive features. ^[1]

Axolotls have 4 (or more) genes for coloration. Wild type means they are either homozygous for the wild coloration or heterozygous for one wild allele and one mutant allele (theoretically, all colors other than wild type originated from a mutation at some point).

D is dark, M is non-melanoid, A is non-albino, and AX is non-axanthic. The D gene makes them dark obviously, with brown/black coloration. The M gene is associated with iridophores, which make them iridescent or shiny. The A gene is associated with true albinism, a lack of pigment, not just white bodies and pigmented eyes like a leucistic. The AX gene is associated with xanthophores, which has to do with yellow and red coloration.

A wild type axolotl is either homozygous or heterozygous for the dominant version of each of those 4 genes. D/D or D/d, M/M or M/m, A/A or A/a, and AX/AX or AX/ax. ^[2]

Axolotls have three different kinds of pigment cells or “chromatophores” that each produces a different color. Iridophore, Xanthophore and Melanophores. ^[3]

Axolotls are easy to study because they survive easily and have very large cells. The cells have different pigmentation so they are easier to keep track of than human cells, which are more difficult to distinguish from each other. They are used as models for development and cancer. One challenging aspect in using it for research is its large genome size, which is about ten times as large as a human genome. The salamanders have already contributed to many important scientific discoveries, such as how cells and organs function and develop in vertebrates, the causes of spina bifida in humans, and the discovery of thyroid hormones. That last discovery is particularly interesting. Researchers in the 1920s fed axolotls thyroid tissue from livestock animals. The hormones cause the axolotls to “grow up” and lose their gills and larval skin. Axolotls occasionally mature on their own as well. ^[4]

In science:
Maybe surprisingly, at first the axolotl was distributed across Europe without being tied to specific research questions, and amateurs engaged in acclimatization and aquarium movements played an important role for the rapid proliferation of the axolotl across the continent. But the aquarium also became an important part of the newly established laboratory, where more and more biological and medical research now took place. Early scientific interest focused on the anatomical peculiarities of the axolotl, its rare metamorphosis, and whether it was a larva or an adult. Later, axolotl data was used to argue both for (by August Weismann and others) and against (by e.g., Albert von K€olliker) Darwinism, and the axolotl even had a brief history as a laboratory animal used in a failed attempt to prove Lysenkoism in Jena, Germany. Nowadays, technical developments such as transgenic lines, and the very strong interest in stem cell and regeneration research has again catapulted the axolotl into becoming an important laboratory animal. ^[5]

These axolotls darken over time. This helps them to maintain camouflage underwater and protect them from predators. The shiny speckles all over the body help differentiate the wild type from the melanoid. ^[6]

They are native to Lake Xochimilco and Lake Chalco, however these lakes do not exist anymore. Mexico City was built on top of them and they were mostly drained. All that remains of the Xochimilco are canals, which are now the only suitable habitat for axolotls. ^[7]