GTP cyclohydrolase II ( gch2 ) and axanthism in ball pythons: A new vertebrate model for pterin‐based pigmentation

Pterin pigments are responsible for many of the bright colors observed across the animal kingdom. However, unlike melanin, the genetics of pterin‐based pigmentation has received relatively little attention in animal coloration studies. Here, we investigate a lineage of axanthic ball pythons ( Python regius ) found in captivity as a model system to study pterin pigmentation in vertebrates. By crowdsourcing shed skin samples from commercial breeders and applying a case–control study design, we used whole‐genome pool sequencing (pool‐seq) and variant annotation. We identified a premature stop codon in the gene GTP cyclohydrolase II ( gch2 ), which is associated with the axanthic phenotype. GCH2 catalyzes the first rate‐limiting step in riboflavin biosynthesis. This study provides the first identification of an axanthism‐associated gene in vertebrates and highlights the utility of ball pythons as a model to study pterin‐based pigmentation.