The Motley mutation cause increased black pigmentation resulting in a completely black or brown boa. This mutation is incomplete dominant and originates from both Central and South American boas. The homologous form of the mutation is expressed when the boa has two homologous alleles of the mutated gene, this is referred to as the “super” form. The super or homologous dominant form of this mutation is lethal within the first two years due to underdeveloped muscles.
When the animal is heterozygous meaning it carries one mutated allele and one normal allele then a completely different phenotype is expressed. The heterozygote will express proteins for each allele and can be considered an intermediate phenotype between wild and “super motley”. The visual heterozygous form of the motley mutation can be easily identified by lateral striping from the neck of the boa through the tail with circles going down the back, as well as a black underside below the vent.