Categories: Pigmentation phene

Links to possible relevant human trait(s) and/or gene(s) in OMIM: 600160 (gene)

Mendelian trait/disorder: yes

Mode of inheritance: Z-linked

Disease-related: no

Key variant known: yes

Year key variant first reported: 2010

Species-specific symbol: B

Species-specific description: Schwochow Thalmann et al. (2017): "feathers of Sex-linked barred chickens are characterized by a fully white bar on a red or black background. . . . Other characteristics of Sex-linked barring are the dilution of dermal pigment in the shanks and beak as well as a white spot on the head present at hatch . . . , which can be utilized for sex determination"

History: This is one of the earliest loci recognised in domestic animals. First reported by Spillman (1908), it later was one of three loci involved in the very first published account of recombination in domestic animals (Goodale, 1917).

Inheritance: Hellström et al. (2010): "Sex-linked inheritance of Sex-linked barring (B*B) and the wild-type (B*N) was reported as early as 1908 (Spillman, 1908)." Schwochow Thalmann et al. (2017): "Available phenotypic data indicate a ranking of the three variant alleles regarding pigment reduction, as follows: Sex-linked extreme dilution [B0]> Sex-linked dilution [B2]> Sex-linked barring [B1]. "

Molecular basis: Hellström et al. (2010) "identified two non-coding mutations in CDKN2A that showed near complete association with the phenotype. In addition, two missense mutations were identified at highly conserved sites, V9D [allele B1] and R10C [allele B2], and every bird tested with a confirmed Sex-linked barring phenotype carried one of these missense mutations." These authors also identified a third allele (B0) "identical to B1 and B2 for the entire 12 kb IBD region except that it has neither the V9D nor the R10C missense mutation". Schwochow Thalmann et al. (2017) showed "that Sex-linked barring is genetically heterogeneous, and that the [four] mutations [reported by Hellström et al., 2010] form three functionally different variant alleles. The B0 allele carries only the two non-coding changes and is associated with the most dilute barring pattern, whereas the B1 and B2 alleles carry both the two non-coding changes and one each of the two missense mutations causing the Sex-linked barring and Sex-linked dilution phenotypes, respectively. The data are consistent with evolution of alleles where the non-coding changes occurred first followed by the two missense mutations that resulted in a phenotype more appealing to humans." These also also report "that one or both of the non-coding changes are cis-regulatory mutations causing a higher CDKN2A expression, whereas the missense mutations reduce the ability of [the CDKN2A-encoded alternate reading frame protein] ARF to interact with [Mouse double minute 2 homolog] MDM2."

Associated gene: