There are 4 main modes of inheritance for “simple” diseases and traits i.e. caused by a single gene: Autosomal Recessive, Autosomal Dominant, X-Linked Recessive and X-Linked Dominant. It is important to understand how these different modes work, and the effect they have on the animal when making breeding plans for your future generations. We have put together these useful graphics to help dog breeders and owner predict the expected genotypes of a litter of puppies bred from a sire and dam with known genotypes for a specific DNA variant.
AFFECTED – The dog has the correct number of copies of the mutation to be affected for the disease/trait being tested for. They will almost certainly develop the disease/trait during their lifetime.
AUTOSOMAL – The mutation is located on one of the autosomes, not on the X or Y sex chromosomes. The disease/trait is not linked to the sex of the animal and affects both males and females equally.
CARRIER – The dog has one copy of the mutation and one normal copy of DNA. These dogs will not develop tested disease/trait. However, they will pass the mutation on to approximately 50% of their offspring. Carriers only occur with diseases or traits with a recessive mode of inheritance. Furthermore, only females can be carriers of diseases or traits that are X-linked recessive.
CLEAR – The dog has two copies of the normal gene and will not develop the disease/trait being tested for. However, we cannot formally exclude the possibility they might develop a similar condition due to other causes or the effect of other, unidentified mutations.
DOMINANT – The disease/trait will affect the dog whether it carries ONE or TWO copies of the mutation. With one copy of the mutation (termed a heterozygote), they will pass the mutation on to approximately 50% of their offspring, causing them to be affected.
RECESSIVE – The disease/trait will affect the dog only when they carries TWO copies of the mutant DNA. If the dog carries one copy of an autosomal mutation (CARRIER) it will not be affected. However, they will pass the mutation on to approximately 50% of their offspring.
X-LINKED – The mutation for the disease/trait is located on the X chromosome and thus affects males and females differently. Females will have 2 copies of the X-linked gene whereas males only have one copy. As a result, males with a single copy of the mutated gene will develop the disease or trait whether it is DOMINANT or RECESSIVE.