The genetics behind the Rhodesian ridgeback's distinctive ridge

The Rhodesian ridgeback is an unmistakable large dog breed with a unique feature—a ridge of hair along its back running opposite to the rest of the coat. This ridge is more than a cosmetic trait; it is the hallmark of the breed's lineage and identity.

The ridge's origin traces back to the breed’s ancestors, including the indigenous Khoikhoi dogs of South Africa, where the distinctive ridge first occurred as a genetic anomaly.

What causes the ridge?

The ridge feature is caused by a specific genetic mutation involving a DNA segment duplication on dog chromosome 18, which includes several genes such as FGF3, FGF4, FGF19, and ORAOV1. This gene duplication influences embryonic development by affecting the way cells proliferate and differentiate, resulting in the characteristic dorsal ridge.

The ridge gene exhibits an autosomal dominant inheritance pattern. This means a dog needs only one copy of the mutated allele to display the ridge. Dogs can be:

• Homozygous dominant (R/R): Carry two copies of the mutation, always passing on the ridge.
• Heterozygous (R/r): One copy of the mutation; usually ridged but can produce ridgeless puppies.
• Homozygous recessive (r/r): No mutation, resulting in ridgeless offspring.

Breeding considerations and the ridge gene

It is possible, though rare, for Rhodesian ridgebacks to be born ridgeless if neither parent passes on the ridge gene. Breeders often consider the absence of the ridge a fault according to breed standards.

Visual inspection alone cannot determine whether a dog carries one or two copies of the ridge gene, making genetic testing essential for responsible breeding to reduce the chance of unwanted ridgeless puppies.

Is there a genetic test for the ridge?

While genetic tests previously were unavailable, current advances now allow breeders to identify the mutation status of individual dogs. This testing helps maintain breed standards and also supports responsible breeding practices.

Health concerns linked to the ridge gene

Despite its distinctive appeal, the ridge gene does associate with certain health issues, notably dermoid sinus, a congenital condition seen almost uniquely in ridged breeds like the Rhodesian ridgeback and the Thai ridgeback. Dermoid sinus can cause serious health problems if left untreated.

The exact biological link between the ridge mutation and dermoid sinus is not fully understood but is believed to be related to the gene duplication affecting embryonic skin development.

Healthy responsible breeding aims to minimise these risks by careful mate selection, genetic testing, and ongoing research collaboration.

Summary

The Rhodesian ridgeback’s ridge is a fascinating genetic trait caused by a dominant gene mutation affecting hair growth along the back. Understanding this genetics helps breeders preserve this unique breed standard while promoting the health and welfare of the dogs. Responsible breeding and awareness of associated health concerns are essential to sustain the breed's quality and longevity.

For those looking to find Rhodesian ridgeback puppies, choosing reputable breeders who test for genetic markers and prioritise health is crucial.