Brittany
29 Brittanys in the atlas. Every number on this page has a source.
29 Brittanys 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 Brittany clusters consistently as Brittany (100% of the 29 dogs here). At the trait loci, HMGA2 runs higher than the atlas average (100% here vs 56%); SMAD2 runs lower than average (31% here vs 74%). Dogs here sit in a relatively sparse region of the atlas, fewer close neighbors than typical.
Low breed predictability score (0.24), individual dogs of this breed vary widely in genetics, suggesting active substructure or sub-population diversity. Only 29 dogs of this breed in the atlas, modestly sampled.
Closest genetic neighbors in the atlas: Weimaraner, Irish Water Spaniel, Petit Basset Griffon Vendeen, Miniature Poodle, and Irish Setter.
What the genome says about Brittany
Computed from the 18,477 research dogs in the Atlas.
- Weimaraner5.04
- Irish Water Spaniel6.43
- Petit Basset Griffon Vendeen6.53
- Miniature Poodle6.92
- Irish Setter7.22
Frequency of the alternate allele in this breed at each locus's representative SNP.
| IGF1 | 56% |
| HMGA2 | 100% |
| SMAD2 | 31% |
| LCORL | 90% |
| STC2 | 52% |
| ADAMTS17 | 73% |
| FGF4·CFA18 | 95% |
| FGF4·CFA12 | 50% |
| RSPO2 | 40% |
| FGF5 | 41% |
| KRT71 | 69% |
| MC1R | 78% |
| MSRB3 | 79% |
| BMP3 | 69% |
| SMOC2 | 67% |
What does the genome say about how a Brittany looks?
Brittanys 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 sits at 56% for the small-body allele. IGF1 is the gene that sets dog body size from Chihuahua to Great Dane. Intermediate frequencies typically keep a breed in the mid-sized range rather than tipping toward the larger working forms.
HMGA2 is near-fixed at 100%, reinforcing the breed's size signal through a second locus on chromosome 10.
SMAD2 sits at 31% at the chromosome-7 height locus.
LCORL is near-fixed at 90%, the NCAPG/LCORL height locus that is one of the strongest single contributors to canine body size.
STC2 sits at 52%.
ADAMTS17 sits at 73%. 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 95%. 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 sits at 50%, the chondrodystrophic variant.
Coat type, length, and color
RSPO2 sits at 40% for the furnishings variant. Furnishings (the eyebrow-and-mustache pattern seen in Schnauzers and Wheaten Terriers) vary across the population at this intermediate frequency, and visible expression depends on the specific allele combination each dog carries.
FGF5 sits at 41% 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 sits at 69% for the wavy/curly variant. Coat curl varies across individuals at this intermediate frequency, and visible expression is also influenced by modifier loci.
MC1R sits at 78% at the representative SNP. MC1R controls the switch between red-to-gold pigment and black-to-brown pigment, with the e/e homozygous genotype producing the gold-to-red spectrum. Substrate frequencies at this SNP depend on the array's polarity, so visible coat color in the breed is a more reliable indicator than this single number.
Ears
MSRB3 sits at 79% for the drop-ear allele, which is why ear set varies across the breed.
Skull shape
BMP3 sits at 69%, contributing to the breed's moderate, mesaticephalic head shape rather than the extreme brachycephalic form.
SMOC2 sits at 67%, contributing to the breed's moderate head shape.
What genetic diseases do Brittanys carry?
From a panel of 250 Mendelian-disease variants screened in 1,054,293 dogs (Donner et al. 2023), Brittanys carry 4 of them at observable frequency. Carrier frequency is not clinical risk. Most recessive variants require two copies for disease expression; many dominant variants show incomplete penetrance. Read this as a population fingerprint of what's in the gene pool, not a per-dog prediction.
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 29 brittanys. We do not have yours.
Every brittany 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).