MyDogDNA Breed Data: Jack Russell Terrier vs Parson Russell Terrier

Both Jack Russell Terriers and Parson Russell Terriers are small, white terriers with black and/or brown markings. These breeds were initially created for bolting fox from their dens during hunts. Both breeds have stayed quite true to their original character of being bold, active, highly driven dogs by being excellent family pets at the same time.

Jack Russell and Parson Russell Terrier history has been quite confusing with different countries having different breed names and standards. Nowadays FCI Jack Russell Terriers are called Russell Terriers in the AKC. Jack Russell Terriers of the JRTCA are called Working Jack Russell Terriers in Europe. JRTCA Jack Russell Terriers and Working Jack Russell Terriers are not considered as official breeds in AKC or FCI. Parson Russell Terriers have the same breed name in FCI and AKC. In this article, we focus on Jack Russell Terrier (FCI Jack Russell Terrier, AKC Russell Terrier) and Parson Russell Terrier breed data created by the MyDogDNA testing panel and compare these two breeds.


One mutation defines these breeds

The most distinct difference in JRT and PRT looks is that Jack Russell Terriers are smaller (breed standard height 25 cms to 30 cms) than PRT (breed standard male ideal 36cm, female ideal 33cm) and have a longer back compared to height than Parson Russell Terriers.

The genetics of this shorter-leggedness of Jack Russell Terriers compared to Parson Russell Terriers might be surprising. The cause for the smaller size of Jack Russell Terriers is in fact the variant causing breed-defining chondrodysplasia. This variant is the key to the appearance with shorter legs compared to height in a large number of small-sized breeds, including not only Dachshunds and Corgis but also for example Coton de Tulear, Miniature Portugese Podengos, West Highland White Terriers and Scottish Terriers.

Jack Russell Terriers typically carry one or two copies of this variant whereas Parson Russell Terriers do not have any copy of this variant. Short-leggedness is inherited dominantly. Since short-legged Jack Russell Terriers can be carriers of the variant causing longer legs, sometimes Jack Russell Terriers with a Parson-like body build are born. Genetic testing can be used to help produce offspring of the desired body build and size.

Coat and colour genetics

Both Jack Russell and Parson Russell Terriers can be either smooth coated, rough (harsh) coated or broken. These coat types are controlled by the furnishings locus. Rough coat results from having two copies of the variant causing furnishings, broken coat is caused by having one copy of the furnishings-variant and dogs with a smooth coat do not have any copy of the furnishings-variant.

Genetics behind coat colour is also the same in both breeds. Piebald is the colour locus that causes the typical largely white coat of JRT and PRT. Piebald hides the basic colour of the dog in most areas of the body and leaves only patches of coloured coat. JRT and PRT are genetically usually either sable, tan pointed, black or saddle tan (typical German Shepherd colour). JRT and PRT with a sable basic colour are white with brown markings. JRT and PRT with tan points have a black muzzle with brown tan points around the eyes and on the cheeks. The patches on the body are usually black but depend on the placement of the patch. Saddle tan JRT and PRT have brown colour on their muzzle and have either brown, black or brown and black coloured patches on their body depending on the placement of the patch. Black JRT and PRT have only black in their coloured patches.

The difference between saddle tan and tan points can be best seen when comparing Rottweiler (tan points) and typical show line German Shepherd colour (saddle tan). The white colour of JRT and PRT hides the underlying colour in most areas but the same pattern is seen in the coloured patches. Sometimes also other colours are seen in JRT and PRT, such as ee-red and bb-brown.

Both breeds have superb genetic diversity – PRT only slightly higher

The genetic diversity of both breeds is high. PRT are only slightly more diverse than JRT, 41.3% vs. 40.4% in heterozygosity. High genetic diversity of these breeds is probably due to their developmental history. These breeds were not created with extreme inbreeding and their breed registries are still open in many countries.

Maintaining and even improving genetic diversity is important for every breed. High diversity protects the dog against genetic disorders by decreasing the risk for inheriting the same recessive disease mutation from both parents. Low genetic diversity increases the risk for autoimmune disorders, and predisposes to inbreeding depression.

Hereditary disorders – frequencies higher in PRT, more disorders found in JRT

Both JRT and PRT are in a good place for preventing hereditary disorders. The genetics behind many hereditary disorders in these has been uncovered making it easy to diagnose and prevent these disorders with simple genetic testing. Here we focus on a few of the most common genetic disorders of these breeds. The full list of tested disorders can be found on the breeds-page.

• Hyperuricosuria, (HUU) Hyperuricosuria predisposes affected dogs to the development of urolithiasis (urate stones) in the kidneys and bladder. Clinical signs of urolithiasis include hematuria, pain while urinating, and blockage of the urinary tract. Hyperuricosuria is inherited in an autosomal recessive manner. The prevalence of this mutation in PRT is 11% and 8% in JRT.

• Primary Lens Luxation, (PLL) Primary lens luxation (PLL) is an inherited condition in dogs that can cause displacement of the ocular lenses. Subluxation, where the lens is partly detached, commonly occurs before complete luxation. Untreated, PLL results in glaucoma, corneal opacities, corneal edema, and blindness. PLL most closely follows an autosomal recessive mode of inheritance though heterozygous dogs also have a low risk of developing PLL. The prevalence of this mutation in PRT is 12 % and 4 % in JRT.

• Spinocerebellar Ataxia (SCA) and Spinocerebellar Ataxia/Late-Onset Ataxia (SCA, LOA) Spinocerebellar ataxia is an early-onset neurological disorder characterised by uncoordinated movements and impaired balance. Two different forms of spinocerebellar ataxia have been described in Jack Russel Terriers and Parson Russel Terriers. It has been suspected that there might be other forms of ataxia in these breeds as well. Both known mutations are in an autosomal recessive manner. The prevalence of these two mutations are around 10% and <1% in PRT, and <1% and <1% in JRT.

• The full list of tested disorders can be found on the Breeds-page.

JRT have slightly lower prevalence for these disorder variants than PRT but more genetic disorders have been found in JRT. The MyDogDNA includes 8 breed-relevant mutation tests for PRT and 9 for JRT. Both breeds are still relatively very healthy.

So which breed is better?

Both breeds are awesome and relatively healthy. Just consider the one that suits your lifestyle better!