Retinopathy in the Swedish Vallhund is a form of progressive retinal atrophy that has a very variable age of onset.
The disorder appears to show an autosomal recessive mode of inheritance. This means that a dog will only develop the disease, associated with the mutation being tested, if it has two copies of the associated mutation (one inherited from each parent).
Individuals with one copy of the mutation and one copy of the normal gene, called carriers, are unlikely to show signs of disease but will pass the mutation onto around half of their offspring.
When two carriers are mated, 25% (on average) of the offspring may be affected by the disease, 25% will likely be clear and the remaining 50% will themselves be carriers.