The gene is the basic unit of heredity. Each gene, acting alone or with other genes, determines one or more canine characteristics. All of the genes that constitute the hereditary makeup of an organism are called the genome.
Genes occur in strands of genetic material within the cell called chromosomes.
A dog is composed of a large number of cells that are genetically identical. Each gene generally occupies a particular position within a particular chromosome. DNA strands are made up of four basic units linked together in pairs. The entire canine genome contains about 3 billion base pairs. Scattered throughout the chromosome are short repeated groups of these base pairs known as microsatellites, or markers, that can be used to track defective genes.