Loss of Hybrid Vigor and Increase in Health Problems after F1. The first-generation (F1) crossbreed is always the healthiest, with the most benefit from hybrid vigor. By crossing different breeds, breeders can eliminate many of the genetically-related health problems that exist as long as the problem genes are not common to both of the breeds involved with the cross. An F1B, or first-generation backcross, typically experience a higher rate of genetic health problems than a first-generation (F1) cross. This is because, in an F1B mating, breeders are recombining the dog's newly created assortment of genes from the F1 cross with one of the original sets of purebred genes, thus increasing the likelihood of reintroducing the recessive genes that create breed-specific health problems. For example, when you combine a first-generation (F1) Labradoodle with a Labrador Retriever, the resulting dog has 75% Labrador Retriever genes. If the Labradoodle has defective genes related to Labrador Retriever inbreeding, it may match up with the defective Labrador Retriever genes to create an F1B with resulting breed-specific health problems. Additionally, by recombining genes with one of the parent breeds, breeders also lose much of the benefit of hybrid vigor. This means that the dog may experience some of the effects of inbreeding depression, including a shorter life span, a depressed immune system, poor temperament, or other issues associated with inbreeding. Creating New Health Problems through Inbreeding. When breeders start a new 'line' of designer dogs by breeding crossbreeds to other crossbreeds of the same type, breeders begin creating the same problems inherent in purebred dogs. Second, third, and subsequent generations of these dogs that are bred to each other result in dogs with limited genetic diversity. This limited genetic diversity begins to be displayed as some of the same genetic diseases as purebreds have when normally recessive disease-creating genes from one dog match up with normally recessive disease-creating genes from the other parent. Over time, these dogs will likely experience some of the same inbreeding depression that their purebred relatives experience. One of the primary benefits of crossbred dogs is in canceling out the effect disease-producing genes have that accumulated over time in the various breeds of purebred dogs. However, after generations of breeding the same type of crossbreed dogs together, these same defective disease-producing genes are more and more likely to 'match up' producing the associated genetic disease. This is especially a concern when breeders try to create crossbreeds according to a breed standard.