The Merle gene is a mutation in the PMEL (Premelanosome Protein) gene that causes unique coat patterns in dogs. The mutation operates in a partial dominance mechanism and leads to significant variation in the color of the dog's coat, eyes, and sometimes skin.

Genetic characteristics

Possible genetic conditions:

1. Mm (one copy of the gene): leads to a characteristic coat pattern of light/dark spots on a basic color background.

2. MM (two copies of the gene): May cause serious health side effects and is therefore prohibited in registered kennels.

3. mm (without Merle gene): Solid colored fur without Merle pattern.

4. Mechanism of action: The Merle gene affects the distribution of pigments in melanocytes, which creates areas of color dilution in the fur.

External expression

• Fur:

• Spotting pattern in varying shades, depending on the base color (e.g.: Blue Merle or Red Merle).

• Eyes: Often light-colored, blue eyes or heterochromia (two different colored eyes).
  
  The Merle gene creates unique traits but requires responsible genetic management to prevent health risks in offspring.