In other species: northern bobwhite , budgerigar

Possibly relevant human trait(s) and/or gene(s) (MIM number): 203100

Mendelian trait/disorder: yes

Mode of inheritance: Autosomal Recessive

Considered a defect: yes

Key variant known: yes

Year key variant first reported: 2000

Species-specific description: "In chickens, three mutant alleles have been reported at the C locus in addition to the wild type allele (C*N), which is the most dominant allele with full pigmentation. These mutations are the red-eye white (C*RE), the recessive white (C*C) and the autosomal albino (C*A) . . . . They all give a white plumage but differ by pigmentation of the eye varying from a grey color to a totally non-pigmented albino phenotype . . . . Furthermore, day-old chicks may exhibit a lightly pigmented down at hatch in homozygous carriers of the C*C mutation. . . . [T]he recessive white (C*C) is one of the earliest traits to be studied in chicken genetics, applying Mendel's rules to segregating families for feather color patterns. The recessive white phenotype is a varietal characteristic of many breeds, such as the Plymouth Rock, Wyandotte, Minorca, Orpington, Jersey Giant, Dorking, Langshan, and Silky" (Chang et al., 2006)

Molecular basis: By cloning and sequencing a very likely comparative candidate gene (based the molecular cause of albinism on other species), Tobita-Teramoto et al. (2000) identified a likely causal variant for the albino allele (C*A) as a "six-nucleotide deletion (−ΔGACTGG) from 817 through 822 bp at codons 237 and 238" of the chicken tyrosinase (TYR) gene as being causative. "This mutation deletes two amino acids in the tyrosinase protein: 237, aspartic acid, and 238, tryptophan."

Chang et al. (2006) reported "that the insertion of a complete avian retroviral sequence in intron 4 of the tyrosinase gene is diagnostic of the recessive white mutation [C*C] in chickens. This insertion causes aberrant transcripts lacking exon 5, and we propose that this insertion is the causal mutation for the recessive white allele in the chicken." Liu et al. (2019) confirmed the effect of this variant.

Associated gene: