The Piebald Gene:
The Piebald gene is responsible for the Jack Russell Terrier's color pattern. Science tells us Jack Russell Terriers as well as other breeds carry the Piebald gene; Bull Terrier, Greyhound, Sealyham Terrier, Beagle, Bulldog, Dalmatian and English Setter - not a complete list but from this you can see that their color patterns are similar.
A piebald's pattern is one of large unpigmented areas now white that would have normally been the color of the dogs natural coat, either black or brown. The color of the animal's skin underneath its coat is also pigmented under the dark patches and unpigmented under the white patches. This color pattern is always irregular and asymmetrical.
Piebald: This pattern consists of a predominantly white dog with small and large patches of color on its head, body and tail. The nose is typically completely black.
Extreme Piebald: This pattern consists of a completely or predominantly white dog with very small amounts of color on its head and sometimes base of tail. A very small body patch may be present too. Sometimes the nose can be partly pink. Extreme white can occasionally cause problems when it removes large amounts of pigment from the face and ears. The most common problem is deafness (due to lack of pigment in certain parts of the inner ear). As well, dogs with exposed unpigmented (pink) skin are also more prone to skin cancer than those with more pigment.
Although deafness is associated with the piebald gene, this is not all of the story. It appears deafness is not inherited as a simple autosomal recessive (or dominant) defect, nor is it X-linked or mitochondrial DNA-linked inheritance. We are still learning about the piebald gene and patterns. Most likely, two genes are involved: piebald and another gene that regulates how strongly the piebald gene is expressed, in other words, how strongly it impacts the dog. We know that deafness occurs at 3-5 weeks after birth, when the blood supply to the cochlea in the inner ear (the stria vascularis) degenerates. This degeneration appears to result from the absence of pigment cells (melanocytes) in the stria. We don't know the role of melanocytes here, but they appear essential. The piebald gene acts by suppressing melanocytes to give white.
We screen all puppies in all liters. If there is any reason for concern with a pup, we will have all pups in the litter hearing (BAER) tested just before they turn seven (7) weeks of age. If a breeder tells you they have never had a deaf puppy, ask if they BAER test their pups… Because if they do not, then they have no way of knowing if they are breeding deaf puppies. BAER testing is the only way you can know for certain.