White spotting patterns that occur in many dog breeds do not have a uniform genetic basis, and the genetics are complex. In piebald/parti/random white spotting, the extent of white pattern expression varies, and markings are often asymmetrical.
The Dominant Black gene (K Locus) affects pigment switching between eumelanin (black) and phaeomelanin (red or yellow) by interacting with the Agouti and MC1R genes.
Several gene variants are known to produce dilute coloration in dogs. Colors are lightened (diluted) to paler shades as a result of the variants' effects on pigmentation.
The melanocortin 1 receptor (MC1R) gene controls production of the pigments eumelanin (black) and phaeomelanin (red/yellow). Six known variants of this gene are responsible for producing markings and coat colors including melanistic mask, grizzle/domino, black, and shades of red/yellow.
Cataracts (clouding of the lens of the eye) are a common cause of blindness in dogs. In Australian Shepherds, a genetic mutation causes hereditary cataracts, which may start forming after 2 years of age and show variable rate of progression and vision impairment.
Chondrodysplasia is a short-legged phenotype characteristic of many dog breeds. Chondrodystrophy, a separate mutation, also includes a short-legged phenotype as well as premature disc degeneration and increased susceptibility to disc herniation.
Loss of cone function due to cone degeneration results in day-blindness and decreased visual acuity. There are 2 known mutations of the CNGB3 gene that cause canine cone degeneration day-blindness in dogs.
