Most of the structures in the human body are composed of protein. The same is true of a dog's body. Moreover, the processes that support life, are regulated by enzymes and hormones, which are themselves specialized proteins. It is no wonder therefore, that the type, location and timing of protein production determines the health, color, size and breed of a dog. Protein production is carried out according to the instructions found in the dog's DNA. DNA is a long chain of nucleic acids that carry the instructions for where, when and how to create all the proteins that make up the muscle, bone, nerves, pigment, etc of a dog's body. It is perhaps easiest to visualize a sentence composed of three letter words. Each three letter word codes for one of the amino acids, the building blocks of protein. A sentence of many three letter words codes for enough different amino acids to create an entire protein. That sentence is comparable to a gene. Each gene contains the information to produce one protein. The genes connect to each other to form a chromosome. Each puppy gets half of its chromosomes from its mother and half from its father. The DNA in those chromosomes is the blueprint for the making of your dog.
Unfortunately, DNA is a molecule that can be injured or miscopied. An injury or miscopying is like writing a nonsensical sentence. If miscopied, a sentence makes no sense, or a gene makes the wrong protein or a malformed protein. A malformed protein cannot perform the function for which it was originally designed, and the puppy with the malformed protein will not be as healthy as a puppy without that mutation. In some cases, it may develop eye disease, bleeding disorders or even cancer. But remember, a puppy gets DNA from both parents. He inherits not single chromosomes, but pairs of chromosomes: one set comes from the egg and one set comes from the sperm. If one chromosome has genes that do not code correctly for making a needed protein, but the second chromosome does make the needed protein, the damage to the puppy can be minimized. Many dog conditions require two mistaken copies of a gene to actually have symptoms of a disease. As long as one gene is correctly making copies of the correct protein, the dog can frequently live a normal, healthy life. These diseases are "recessive." . Obviously, dogs from different backgrounds, with different "bad genes" in their family of origin are less likely to give the same bad gene or chromosome to their offspring.
Pure bred dogs come from a long history of breeding similar dogs to each other, which is why some dog diseases/conditions occur more frequently in one breed than in another. When two totally unrelated dogs are bred together, as is the case when two separate breeds are bred together, there is "Genetic diversity," meaning they have different gens, including different "bad genes." When these two entirely different breeds, as cocker and poodle or golden retriever and poodle, are bred together, the offspring they produce are referred to as the F1 generation. The puppies in the F1 generation will have greater genetic diversity than later generations because the background of their parents is the most different. This difference in back ground between the parent dogs is responsible for what is known as hybrid vigor, and the greatest hybrid vigor is in this F1 generation. While there are decided advantages of breeding a puppy from that litter back to a poodle, the first F1 litter will always have the most dependable hybrid vigor, though not necessarily the most consistent non shedding coat.
In the case of goldendoodles, but really in the case of any doodle, the parents are known to have a certain frequency of some genetically recessive diseases. If a disease is "recessive," that means two "bad genes" are needed in order to show symptoms of the disorder. If both parents appear healthy, that is, do not have the disease/disorder, it might be assumed that their progeny will not have the disorder. However, if both parents "carry" the "bad gene," but just one copy, they will appear completely normal and still have the ability to produce progeny that get two "bad" genes, one from each parent, and have symptoms of the disease/disorder. There are numerous diseases caused by recessive genes in the golden retriever breed. There are different diseases caused by recessive genes in the standard poodle breed. Because many of those genetically influenced diseases are not mutually present in the two breeds, crossing a poodle with a golden retriever is less likely to result in the occurrence of two "bad genes" and one of those diseases than when a poodle is bred to a poodle or a golden retriever bred to a golden retriever. The same exact principle holds true for bernedoodles, englishdoodles and labradoodles, making all hybrids healthier than their respective pure bred parents.