[3] Further characteristics of sex-linked barred chickens are the dilution of skin pigment in the legs as well as a white dot at the top of the head of freshly hatched chicks which can be used for autosexing: homozygous males have a much bigger spot than hemizygous females.
[3] The responsible gene was predicted to be located on the Z chromosome[7][8] and since male birds are homogametic (ZZ), they can be either hetero- or homozygous for sex-linked barring.
In 2010 Swedish scientist have identified four mutations located in or around the tumor suppressor locus CDKN2A, which appear to be associated with sex-linked barring.
[9] This phenotype has been initially described as a distinct but closely related mutation,[10] however, it was later assigned to the same gene and termed ‘Sex-linked Dilution'.
With more of the gene product, which is called ARF (Alternate Reading frame Protein) in the cell, more of p53 is protected from degradation.
[11] Both missense mutations lead to a malfunctioning ARF protein, which is counteracting the effect of the higher activity of the gene to some degree.
It is intriguing that chickens carrying the B1 or B2 allele with a malfunctioning ARF do not show any higher prevalence to any type of cancer and are usually considered very sturdy and easy to keep breeds.
It is also astonishing that the majority of the egg and meat production industry is relying on chickens, which have a defect in a tumor suppressor gene.