Autosomal dominant traits are those that are expressed even though the pair of alleles are not matched.  Therefore, only 1 parent need possess the dominant trait to pass it on to his or her offspring.  In order for an autosomal dominant trait to be inherited 1 of the parents must also be affected. Autosomal dominant genetic diseases are easily prevented simply by removing affected dogs from the breeding pool.  

Autosomal recessive traits are more complicated.  Recessive traits can only be expressed when a matched pair of alleles (one of each parent) combine to form the gene responsible for the trait. Therefore both parents of the affected puppy must be carriers.  Recessive traits tend to occur in one generation and then skip one or two generations until carrier descendants are again mated. The zinc responsive dermatosis reported in a Hedlund female is a known autosomal recessive genetic disorder that had apparently skipped several generations and thus had not been previously reported within the line.

On average, a litter from a mating between two carriers will result in about 25% of the puppies being affected, and 50% of the puppies in the litter will be carriers.  If the disease is one for which no genetic test is available and there is no other way to determine which puppies may carry the recessive allele, all siblings of an affected puppy should be considered potential carriers and be bred only to dogs that are unlikely to also be carriers.  

Sex-linked traits are inherited via the single allosome (sex linked chromosome) and are nearly always on the X-chromosome.  On average, half of the male offspring of a carrier dam are affected with the trait.  The trait may skip generations.  Affected males transmit the gene to all of their daughters (rendering them carriers) and to none of the sons.  If both parents are affected by the trait, all of the offspring will also be affected.  For an affected female offspring to occur the dam must be at least a carrier and the sire must be affected with the trait.  

It is in our favor that the heritable diseases that resulted in the overbite and laryngeal dysfunction recognized in Hedlund Huskies are probably polygenic or multifactorial traits.  Polygenic traits are controlled by two or more genes (usually by many different genes) at different loci on different chromosomes while multifactorial traits require both a genetic propensity and an environmental trigger to be expressed.  Hip and elbow displasia are polygenenic traits seen in many dog breeds.

As with autosomal recessive traits, both the sire and dam must contribute the mutated genes that cause the trait to occur in the offspring.  Unlike recessive traits, however, the contribution from the sire and dam need not be equal.  Because we don’t yet know the number or the specific effect of the genes involved in polygenic traits in dogs, no predictable ratios can be associated with those traits.  Polygenic traits may skip generations and may appear to be erratic in occurrence. 

By addressing polygenic diseases in the same manner as autosomal recessive traits, we believe we can eventually reduce the numbers of affected puppies produced in each generation.