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Merle in Chihuahuas


Breeders often debate whether Merle Chihuahuas should be bred, given the potential health risks associated with the Merle gene. Some claim Merle was introduced into Chihuahuas through crossbreeding, while others argue it has been part of the breed for decades. This article provides clarity based on historical evidence and genetic research.

History of Merle in Chihuahuas

Historical records indicate that Merle Chihuahuas have existed for over 75 years. Milo Denlinger's first edition of "The Complete Chihuahua" in 1947 documents Merle Chihuahuas, suggesting that this pattern is not a recent introduction but has a longstanding presence in the breed【Denlinger, M.G. (1947). The Complete Chihuahua.】.

Genetic Basis of Merle

The Merle gene affects pigmentation and is responsible for the mottled coat patterns seen in many breeds, including Chihuahuas. It is a semi-dominant gene located at the PMEL locus (also known as SILV). Dogs with one copy of the Merle allele (Mm) exhibit the Merle pattern, while those with two copies (MM), known as double Merles, are at a high risk of severe health issues​ (PLOS)​​ (American Kennel Club)​.

Health Concerns with Merle

Breeding two Merle dogs together can result in double Merle puppies, which are prone to significant health problems such as deafness, blindness, and various other defects. This is due to the impact of the Merle gene on pigmentation in critical areas like the eyes and ears. Therefore, it is recommended to avoid Merle-to-Merle breedings unless genetic testing can accurately assess the risk​ (BMC blog network)​​ (American Kennel Club)​.

Misconceptions About Merle Inheritance

Many breeders mistakenly believe that Merle markings can be inherited even if none of the parents display the Merle pattern. However, this is not genetically accurate:

  1. Merle Cannot Skip Generations: The Merle pattern is directly tied to the presence of the Merle allele. A Chihuahua can only display the Merle pattern if it inherits one Merle allele from a parent. Therefore, it is impossible for a Merle Chihuahua to be produced unless at least one parent is Merle​ (PLOS)​​ (American Kennel Club)​.

  2. Cryptic Merles: Some Merle dogs may not show obvious Merle patterns due to their base coat color masking the Merle patches, known as cryptic Merles. These dogs can still pass the Merle gene to their offspring, but again, one parent must carry the Merle allele​ (PLOS)​​ (American Kennel Club)​.

Responsible Breeding Practices

DNA Testing: Always test your breeding stock to confirm their Merle status. This helps in making informed decisions and preventing accidental double Merle breedings.

Accurate Registration: Ensure that your dogs are accurately registered with their correct color and pattern information.

Transparency: Be open about the genetic makeup of your breeding dogs, especially if they are Merle or can produce Merle offspring.

Breeding Strategies: It is possible to breed Merle to Merle if you can determine the frequency and specific alleles involved, such as Mc (Cryptic Merle) and Ma (Atypical Merle). However, careful genetic testing and responsible practices are crucial to mitigate health risks​ (PLOS)​​ (BMC blog network)​.


With the right knowledge and precautions, Merle Chihuahuas can be bred responsibly. Understanding the genetics and historical context of the Merle gene helps breeders make informed decisions that prioritize the health and well-being of their dogs. By employing responsible breeding practices, breeders can maintain the integrity of the Chihuahua breed while avoiding the severe health issues associated with improper Merle breeding.

For more detailed information on the Merle gene and responsible breeding practices, you can refer to peer-reviewed studies and resources from reputable genetics research organizations​ (PLOS)​​ (BMC blog network)​​ (American Kennel Club)​.


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