Categories: Pigmentation phene

Links to possible relevant human trait(s) and/or gene(s) in OMIM: 172800 (trait) , 164920 (gene)

Mendelian trait/disorder: yes

Mode of inheritance: Autosomal dominant

Disease-related: no

Key variant known: yes

Year key variant first reported: 2012

Species-specific symbol: I^Be

History: This trait was first studied by Spillman (1907).

Inheritance: Spillman (1907) postulated that the belt phenotype required a dominant allele at each of two autosomal loci. By the early 1980s, the trait was regarded as single-locus autosomal dominant (Ollivier and Sellier, 1982). The results of Rubin et al. (2012) indicate four alleles at this locus, namely Wild-type, Dominant white (OMIA 000209-9825), Patch (OMIA 001743-9825) and Belt (this entry). (with thanks to Leif Andersson)

Mapping: From a genome scan with 65 microsatellite markers on 67 backcross offspring from matings between non-belted sires and F1 (belted x non-belted) dams, Giuffra et al. (1999) linkage-mapped the belt locus to the centromeric region of chromosome SSC8, which contains two potential candidate genes, namely KIT and EDNRA. They then showed complete co-segregation of the belt phenotype with a SNP at position 2678 of exon 19 of the KIT gene, which strongly suggested that belt is an allele at the KIT locus. This study established for the first time that Belt is an allele to the Dominant white allele (see OMIA 000209-9825). Before this study Belt and Dominant white were considered to be two independent loci in the pig. (with thanks to Leif Andersson)

Molecular basis: Utilising extensive genome sequence data from tens of pigs, Rubin et al. (2012) showed that Hampshire pigs (belted phenotype) have "a 4.3-kb duplication (DUP2) located ∼100 kb upstream of KIT and a 23-kb duplication (DUP3) ∼100 kb downstream of KIT, which in turn contained a fourth ∼4.3-kb duplication (DUP4) not present on wild-type chromosomes". Across four breeds, belted pigs always had DUP2 and DUP4, but some lacked DUP3. The authors "conclude that DUP2–4 is strongly associated with the presence of the Belt and propose that one or more of these duplications are required for manifestation of the Belt phenotype . . . DUP2 is the strongest causative candidate because it overlaps with one of the most well-conserved noncoding regions located upstream of KIT". Fontanesi et al. (2016) identified a "SNP (g.43597545C>T; position on porcine chromosome 8 in the Sscrofa10.2 genome assembly)". The authors reprted that "Allele T was almost fixed in [the belted] Cinta Senese [breed] (95.9%) and absent in many breeds and was considered the tag SNP of the belted allele". By genotyping "the SNP rs328592739 in Krškopolje, Cinta Senese and Swäbisch-Hall belted pigs" and by studying whole-genome sequence data from a wide variety of breeds, Ogorevc et al. (2017) showed that this SNP "is not associated with white belt phenotype across different [other than Cinta Senese and Hampshire] pig breeds".

Breeds: Cinta Senese, Italy (Pig) (VBO_0013055), Essex, United Kingdom of Great Britain and Northern Ireland (Pig) (VBO_0016873), Hampshire Down (Sheep) (VBO_0001431), Schwäbisch Hällisches Schwein, Germany (Pig) (VBO_0012910), Wessex Saddleback (Pig) (VBO_0001211).
Breeds in which the phene has been documented. (If a likely causal variant has been documented for the phene, see the variant table breeds in which the variant has been reported).

Associated gene: