The more variation, the more genetic degradation

40% of mixed-breed dogs are carriers for at least 1 of the known genetic diseases

https://www.americanveterinarian.com/news/online-database-of-canine-inherited-genetic-disorders-now-available

Excerpt: "Using a custom-designed beadchip microarray, 83,220 mixed-breed dogs and 18,102 purebred dogs representing 330 breeds were examined for 152 known disease variants, including progressive retinal atrophy, hyperuricosuria, collie eye anomaly, multidrug sensitivity, exercise-induced collapse, and von Willebrand’s disease.

“For owners, understanding for which genetic diseases their dog is at risk for can help them and their veterinarians design a personalized care and wellness program for their dog,” Dr. Donner said.
 
The 3 body systems found to be the most commonly affected across both purebred and mixed-breed dogs were the vision, nervous, and circulatory systems.

Study results showed that approximately 2 in 5 dogs carried at least 1 copy of a tested disease variant. Furthermore, most disease variants were shared by both mixed-breed and purebred dogs. Other key findings included the following:

• Approximately 2% of mixed-breed dogs are at risk of becoming affected and 40% are carriers for at least 1 of the diseases.
• Approximately 5% of purebred dogs are at risk of becoming affected and 28% are carriers for at least 1 of the diseases.

This means that while mixed-breed dogs are less disease-prone than purebred dogs, they are more likely than purebred dogs to be carriers of the recessive disorders studied. According to the study authors, this provides DNA-based evidence for hybrid vigor, or outbreeding enhancement.
 

“A dog carrying an inherited disorder is not a ‘bad dog,’” the study authors wrote, “but we humans responsible for breeding selections do need to make sustainable decisions avoiding inbreeding, ie, mating of dogs that are close relatives.”"

My comment: Dog breeding means artificial selection of certain characteristics of the dog breed. At molecular biological level this means epigenetic amplification or silencing of certain epigenetic information patterns and markers associated with certain characteristics. When two different dog breeds are mixed, then the epigenetic profiles are altered and shifted within the offspring and this results in several DNA mutations.

This same phenomenon can be observed in nature as well. The more ecological adaptation and variation, the more genetic degradation. That's why evolution is not happening. Any change in organisms is based on epigenetic regulation of existing biological information OR gradual but inevitable corruption of information. Don't get lost.