Australian Shepherd
The merle allele, which produces a mingled or patchwork combination of dark and light areas, is the coat pattern most commonly associated with the breed. This merle (M) is dominant, so heterozygous dogs (Mm) show the pigmentation pattern; however, when two merles are bred, the statistical risk is 25% of the offspring will end up with the two copies of the merle gene (homozygous). These dogs usually have a mostly white coat and blue irises and are often deaf, blind, or both. In this case, the deafness and blindness are linked to having two copies of the merle gene, which disrupts pigmentation and produces these health defects. The tri-colored (red, black, and white) Merles will have a 1/4 chance of being blind because of the genes when breeding two Merle colored dogs for the recessive fur color.