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."

Associated gene: