Homozygous Merles
Homozygous merles or double merles may only result when a merle is bred to another merle and the puppy receives 2 copies of the merle gene; 1 from each parent. It is very important to note that although a dog may visually be a none merle, it is still possible for it to genetically be a merle. Homozygous merles will not have any health risks associated with merle to merle breeding, if the genetic merle lengths of their parents are compatible. This is DNA testable through M Locus and must include merle length.
Homozygous merles with incompatible merle lengths usually have excessive white coloration and may also be born blind, deaf, disfigured, and with partial or missing eyes and/or organs. These puppies are often destroyed immediately after birth due to the high risk of impending health problems. This breed detriment is completely preventable through DNA testing and responsible breeding.
Not to be confused with homozygous merles, pattern whites have excessive and/or unacceptable white coloration due to whitehead and/or piebald genetics.
Piebald is DNA testable through S Locus, whitehead is not currently testable.
Extra attention should be given to loss of coloration surrounding the eyes and ears. This loss of pigment is directly related to a heightened risk of deafness.
Hartspride does not breed incompatible merle to merle and only breeds dogs with acceptable and/or minimal white.
For more information regarding homozygous and pattern whites please click the link below:
https://www.australian-shepherd-lovers.com/lethal-white.html