Current progress
*****Our scientific paper describing the genetic basis of three color morphs is available on bioRxiv!*****
Melanin
Image credit: WikipediaMorphs affecting melanin
We focused our initial studies on ball python color morphs showing a reduction in brown-to-black coloration in the skin and eyes. This trait is characteristic of a defect in production of the pigment melanin. Melanin is a brown-to-black pigment present throughout the animal kingdom, including in humans. Morphs showing a reduction in melanin include Albino/Toffee/Candy (allelic), Lavender Albino, and Ultramel. The reduction in melanin is most severe in Albino, followed by Lavender Albino and Ultramel. Toffee and Candy are allelic with Albino, but their reduction in melanin is less severe than Albino.
Child with albinism and his mother, who is unaffected by the condition
Photo credit: Ana Yturralde via doi.org/10.1111/pcmr.12167
Hypothesis: Genes linked to albinism in humans are the same as genes causing color morphs in ball pythons.
Defects in melanin production in humans cause a genetic condition known as albinism (technically, 'oculocutaneous albinism'). Albinism in humans ranges from severe to mild, depending on the genetic cause.
The genes responsible for albinism in humans are shared with ball pythons. These genes encode proteins required for producing melanin. We predicted that the genes responsible for albinism in humans were the same as the genes causing the Albino/Toffee/Candy, Lavender Albino, and Ultramel color morphs in ball pythons.
Method: Compare gene sequences between normal ball pythons and color morphs
To test our hypothesis, we selected seven genes known to cause albinism in humans. We sequenced the coding regions of these genes in a normal ball python and again in animals belonging to each color morph. We then compared the gene sequences between animals. We focused on the coding regions of the genes because the coding regions are the parts of a gene that determine the structure and function of the protein that the gene encodes. Mutations that disrupt gene function often (but not always) reside in coding regions.
Genetics of Albino, Toffee, and Candy
We discovered that the Albino, Toffee, and Candy color morphs are caused by variants in the gene TYR. This gene encodes an enzyme called tyrosinase.
Tyrosinase is responsible for catalyzing the first step of a biochemical pathway that converts the amino acid tyrosine into melanin. Albino, Toffee, and Candy animals carry genetic variants that make the enzyme non-functional (or less functional). As a consequence, Albino, Toffee, and Candy animals produce no melanin or very little melanin.
Albino
Photo credit: Lucy's (via MorphMarket)
Toffee
Photo credit: Taylor Made Morphs (via MorphMarket)
Candy
Photo credit: NERD (via MorphMarket)Albino vs. Toffee vs. Candy
Ball python breeders consider Albino, Toffee, and Candy to be different alleles of the same gene. Is this idea true? Yes and no. Yes, these morphs are all caused by variants in the same gene (the gene TYR). But no, these morphs do not necessarily correspond to different molecular alleles. The 'Toffee' and 'Candy' morphs appear to be caused by the same allele. We hypothesize that this morph was discovered twice and named 'Toffee' by one person and 'Candy' by another person. In addition, the morph described as 'Albino' is actually made of up two different molecular alleles. Some Albinos carry one allele; some Albinos carry the other allele; and some Albinos carry one copy of each allele. We hypothesize that the two alleles making up the 'Albino' morph produce similar color patterns and were not previously recognized by breeders as distinct.
Genetics of Lavender Albino
We discovered that the Lavender Albino morph is caused by a deletion in the gene OCA2. This gene encodes a protein responsible for maintaining the pH of the melanosome (the cellular structure where melanin is produced). Lavender Albinos cannot control of pH of this structure. As a result, the enzymes that produce melanin are less active, and less melanin is produced.
Genetics of Ultramel
We discovered that the Ultramel color morph is caused by variants in the gene TYRP1. This gene encodes an enzyme involved in synthesizing melanin. Mutations in this gene in humans cause a form of albinism in which individuals have reddish hair. This form of albinism in humans is more mild that other forms of albinism, similar to the difference between the Ultramel color morph and the Albino and Lavender Albino color morphs.
Caramel Albino
Photo credit: CV Exotics (via MorphMarket)
Ultramel vs. Caramel Albino
We discovered that the Ultramel color morph has two alleles. We hypothesize that one of these alleles may represent the morph originally described as Caramel Albino. Caramel Albino animals look similar to Ultramels, and we hypothesize that the two morphs are allelic. We suspect that some animals described as Ultramels are actually Caramel Albinos.
To test our hypothesis, we need samples of Caramel Albinos. If you own a Caramel Albino animal, please send us a shed from your animal!