Chromosome - Chromosomes are found in the nucleus of every living cell. The genetic information needed to produce a dog is contained in exactly 78 chromosomes.  The sire and dam each contribute 39 chromosomes to their offspring.

Constitution - The manner in which an individual dog reacts to external or environmental influences.

Dominant - The genetic information for a particular trait form one parent, e.g., eye color, that supersedes the genetic information from the other parent for the same trait.

Familial - Traits which run in certain lines or groups of dogs.

Gene - A basic unit of heredity.  Chromosomes contain many genes, and each gene is responsible for determining part of all of a trait.  Recent discoveries in genetic science have shown that there may be as many as 100,000 pairs of genes contributing to the construction of a dog, and 200,000 contributing to the construction of a human being.

Genotype - Genes that are carried by a dog but not necessarily seen or expressed.

Heredity - The traits a puppy acquires from its parents.  These traits may be obvious or they may be hidden, yet passed on to subsequent generations.

Hybrid - A dog with different genes for the same trait.

Inbreeding - Breeding dogs which have the same or nearly the same genetic makeup.  Breeding litter mates is the purest example of inbreeding.

Linebreeding - Currently, dog breeders think of linebreeding as a mating of dogs that have the same parent or grandparent.  Linebreeding was used extensively by pioneer breeeders of purebred dogs because the deformities that occurred through inbreeding resulted in a general belief that the entire process was bad.  Early breeders felt that linebreeding achieved the same results but took longer.

Mutation - A mutation occurs when a gene reproduces a copy of itself that is not identical.

Outcrossing - Dog breeders expect this word to be defined as the mating of unrelated dogs.  Since this is theoretically impossible within a pure breed (all French Bulldogs are related simply because they are French Bulldogs), outcrossing has come to mean breeding dogs that do not have the same parent or grandparent.

Phenotype - Genes that express themselves in the observable, physical characteristics of the dog.

Prepotent - A term applied to a stud dog or a brood bitch when that dog or bitch transmits genes which do not "skip a generation," are found in the majority of the puppies, and are further transmitted by their progeny.  The term prepotent was used to describe dogs long before breeders were aware of Mendel's theories of dominant and recessive genes.

Purebred - A dog with identical genes for the same trait.

Recessive - A gene that does not manifest itself in the outward appearance of a dog when paired with a dominant gene.

Trait - A physical or temperamental characteristic, such as eye color, leg length or shyness.