Bull Terrier
44 Bull Terriers in the atlas. Every number on this page has a source.
44 Bull Terriers in the Sniff Atlas. Population-genetic snapshot, Mendelian carrier frequencies from Donner 2023, and the data substrate's release version, sample sizes, and evidence tier on every claim.
In the atlas, the Bull Terrier clusters consistently as Bull Terrier (100% of the 44 dogs here). Genetic diversity is low (mean heterozygosity 0.196), suggesting a tightly-related local population. At the trait loci, SMOC2 runs lower than average (2% here vs 75%); HMGA2 runs lower than average (7% here vs 56%). Dogs here sit in a relatively sparse region of the atlas, fewer close neighbors than typical.
Ranks 5 of 107 on the bottleneck severity scale, among the most genetically contracted breeds in the atlas. Mean heterozygosity is 0.196, low even for a closed-stud breed. High breed predictability score (5.01), individual dogs of this breed reliably cluster together genetically.
Closest genetic neighbors in the atlas: Miniature Bull Terrier, Bullmastiff, Staffordshire Bull Terrier, Boston Terrier, and Bulldog.
What the genome says about Bull Terrier
Computed from the 18,477 research dogs in the Atlas.
- Miniature Bull Terrier30.10
- Bullmastiff47.88
- Staffordshire Bull Terrier63.73
- Boston Terrier68.54
- Bulldog69.31
Frequency of the alternate allele in this breed at each locus's representative SNP.
| IGF1 | 89% |
| HMGA2 | 7% |
| SMAD2 | 51% |
| LCORL | 93% |
| STC2 | 97% |
| ADAMTS17 | 32% |
| FGF4·CFA18 | 85% |
| FGF4·CFA12 | 97% |
| RSPO2 | 86% |
| FGF5 | 44% |
| KRT71 | 99% |
| MC1R | 97% |
| MSRB3 | 99% |
| BMP3 | 99% |
| SMOC2 | 2% |
What does the genome say about how a Bull Terrier looks?
Bull Terriers look the way they do because of a small set of fixed and near-fixed morphology genes that, taken together, define the visible breed. Each translation below pairs the gene with the trait an owner actually sees, the breed's allele frequency at that locus, and a one-clause causal phrase.
Size and build
IGF1 is near-fixed at 89% for the small-body allele, which keeps the breed compact relative to its working-line ancestors.
HMGA2 is at 7%, leaving most of the size signal to other loci in the panel.
SMAD2 sits at 51% at the chromosome-7 height locus.
LCORL is near-fixed at 93%, the NCAPG/LCORL height locus that is one of the strongest single contributors to canine body size.
STC2 is near-fixed at 97%, modulating growth-axis signaling toward the breed's body-size set point.
ADAMTS17 sits at 32%. ADAMTS17 is a body-size locus also linked to lens disorders.
Leg length
The FGF4 retrogene on chromosome 18 is near-fixed in this breed at 85%. This is the leg-length variant. The breed is fully committed to the long-legged form rather than the short-legged Corgi-and-Dachshund body plan.
The FGF4 retrogene on chromosome 12 is near-fixed at 97%, the chondrodystrophic variant associated with intervertebral disc disease risk in breeds that carry it.
Coat type, length, and color
RSPO2 is near-fixed at 86% for the furnishings allele, the genetic basis of the eyebrows-and-mustache pattern seen in Schnauzers and Wheaten Terriers.
FGF5 sits at 44% for the long-coat variant. Coat length is influenced by other loci as well, so intermediate FGF5 frequencies do not always correspond to intermediate visible coat lengths.
KRT71 is near-fixed at 99% for the wavy/curly variant. Coat curl phenotype varies across breeds at this fixation depending on modifier loci, and visible expression is not always curled even when the locus is fixed.
MC1R is at 97% at the representative SNP. MC1R controls the switch between red-to-gold and black-to-brown pigment, with the e/e homozygous genotype producing the gold-to-red spectrum by blocking eumelanin (black and brown pigment).
Ears
MSRB3 is at 99% for the drop-ear allele, the genetic basis of the breed's signature dropped ear set.
Skull shape
BMP3 is at 99%, contributing to the breed's brachycephalic skull shape.
SMOC2 is at 2%, leaving the breed in the long-headed dolichocephalic form.
Where every number on this page came from.
This page draws on three primary data sources. Carrier frequencies for the Mendelian section come from Donner et al. 2023 (CC-BY-4.0). We grade these data at evidence Limited because the cohort is a direct-to-consumer ascertainment, which biases toward owners who chose to test their dogs. The panel also uses tag-SNP proxies for some variants rather than direct causal-variant assays. Limited is a study-design grade, not a quality grade: the Donner cohort is the largest open canine-genotype dataset in existence and we are grateful for it. We rate the confounding MEDIUM.
Population-genetic dimensions (heterozygosity, intra-breed PCA distance, nearest neighbors, trait-locus frequencies) come from CanVAS (Brundage 2026), harmonized through the Sniff Atlas. The exact release date and verification commit are pinned at the bottom of the page so a researcher can trace a number back to a specific snapshot. The disease-gene-variant graph comes from OMIA (Online Mendelian Inheritance in Animals; Nicholas, Tammen, and the Sydney Informatics Hub at the Sydney School of Veterinary Science, The University of Sydney; retrieved April 2026, DOI 10.25910/2AMR-PV70).
What this page does not yet have. Inheritance modes and per-disease penetrance evidence from Donner 2023 are now in the structured data for every variant the panel covers. Mondo, OMIM, Ensembl, and HGNC cross-references on gene pages remain pending — they arrive in December 2026 alongside the imputed 9.67M-variant CanVAS dataset via the OMIA SQL dump absorption. Until then, gene IDs carry NCBI Gene and OMIA phene URLs only; the wider human-homolog and disease-ontology cross-reference set fills in with that release.
How to cite this page. The computed dimensions on this page are derived from the open Sniff Atlas v1.0.1 (Gehring 2026, doi:10.5281/zenodo.20566358, CC-BY 4.0). Full citation formats including BibTeX, RIS, and CITATION.cff at sniff.world/cite.
We have 44 bull terriers. We do not have yours.
Every bull terrier added sharpens the breed's genetic neighborhood. Enrollment is free. The data stays open. The star is permanent.
- Donner J, Anderson H, Davison S, et al. (2023). Frequency and distribution of 152 genetic disease variants in over 1,000,000 mixed-breed and purebred dogs. PLOS Genetics 19(2):e1010651. doi:10.1371/journal.pgen.1010651
- Brundage J, et al. (2026). CanVAS: a harmonized canine variant atlas. bioRxiv. doi:10.64898/2026.04.13.718238
- Nicholas, F.W., Tammen, I., & Sydney Informatics Hub. (2026). Online Mendelian Inheritance in Animals (OMIA) [dataset]. The University of Sydney. https://omia.org. doi:10.25910/2AMR-PV70 (retrieved April 2026).