Categories: Pigmentation phene

Links to possible relevant human trait(s) and/or gene(s) in OMIM: 605513 (gene)

Mendelian trait/disorder: yes

Mode of inheritance: Z-linked incomplete dominant

Disease-related: yes

Key variant known: yes

Year key variant first reported: 2020

Species-specific symbol: St

Species-specific description: Bruders et al. (2020): "The classical pigmentation pattern in C. livia known as Almond is caused by a semi-dominant mutation (St allele) at the sex-linked Stipper (St) locus [Wriedt and Christie, 1925] . . . . Unlike most other pigmentation pattern traits in pigeons, the variegated or sprinkled patchwork of plumage colors in Almond is apparently random within and among individuals . . . Furthermore, the color pattern changes in an unpredictable manner with each molt [Hollander and Cole, 1950; Hollander, 1942; Quinn, 1971]. The number of pigmented feathers in Almond pigeons also increases with each successive molt, and this effect is more pronounced in males . . . . Notably, this phenomenon is the opposite of what is typically observed with pigmentation traits that change throughout the lifespan of an individual, such as vitiligo and graying, which result in a decrease in pigment over time . . . . In addition to Almond, at least six other alleles at St lead to varying degrees of depigmentation in pigeons, suggesting that the St locus might be a mutational hotspot".

Inheritance: Bruders et al. (2020): "Almond is a sex-linked, semi-dominant trait controlled by the classical Stipper (St) locus. Heterozygous males (ZStZ+ sex chromosomes) and hemizygous Almond females (ZStW) are favored by breeders for their attractive plumage. In contrast, homozygous Almond males (ZStZSt) develop severe eye defects and often lack plumage pigmentation, suggesting that higher dosage of the mutant allele is deleterious."

Molecular basis: Bruders et al. (2020) "found a copy number variant (CNV) within the differentiated region that captures complete or partial coding sequences of four genes, including the melanosome maturation gene Mlana. We did not find fixed coding changes in genes within the CNV, but all genes are misexpressed in regenerating feather bud collar cells of Almond birds. Notably, six other alleles at the St locus are associated with depigmentation phenotypes, and all exhibit expansion of the same CNV."

Associated gene: