Categories: Pigmentation phene

Links to possible relevant human trait(s) and/or gene(s) in OMIM: 611740 (gene)

Mendelian trait/disorder: yes

Mode of inheritance: Autosomal recessive

Disease-related: no

Key variant known: yes

Year key variant first reported: 2008

Species-specific name: Yellow skin; Yellow shanks

History: This trait was one of the five first animal traits (all in chickens) whose Mendelian inheritance was documented (by Bateson and Saunders, 1902; pages 87-124) after the rediscovery of Mendel's result. The other four traits are Rose-comb (OMIA 000884-9031), Pea-comb (OMIA 000782-9031), Polydactyly (OMIA 000810-9031), and Dominant White (OMIA 000373-9031).

Inheritance: Know (1935) confirmed that yellow skin (most visible as yellow shanks) in chickens is due to homozygosity for a recessive autosomal allele.

Molecular basis: By some excellent biological detective work, Eriksson et al. (2008) have shown the yellow-skin gene to be the gene encoding beta-carotene oxygenase 2 (BCO2). Interestingly, the yellow allele that is so common in domestic chickens throughout the world actually originates not from the red jungle fowl but from the grey jungle fowl, thereby indicating a hybrid origin of the domestic chicken. Because there are so many difference in the sequence between the two alleles, the actual causal difference has not yet been identified but it must be regulatory, since the authors show that the yellow skin allele is expressed in liver but not in skin. Wang et al. (2023): "Scanning for the presence of skin color related SNPs (G>A chr24: 6,264,085 bp, A>G chr24: 6,273,428 bp and G>A chr24: 6,287,900 bp, WUGSC 2.1/galGal3) between yellow-skin and white-skin chicken did not lead to the identification of previously reported SNPs [Eriksson et al. 2008]. An explanation for this discrepancy may be related to differences in the chicken breeds used in the two studies. Instead, we found a new SNP in the BCO2 gene, which, when tested in other Chinese indigenous chicken breeds, may be used as a genetic marker associated with skin color. The G/A mutation found in exon 6 of BCO2 (c.890A>G, GenBank accession No. XM_417929.6) was a same-sense mutation and did not directly change the amino acids of protein, but they were not entirely negligible either, as they affected BCO2 gene expression."

Associated gene: