Breeders, who cross two purebreds, producing the first generation of hybrids, believe in the power of the heterosis effect and hybrid vigor. Vigor implies "physical or mental strength, energy, or power."
Let's be more specific of what does this heterosis effect mean.
The theory of hybrid vigor suggests that the same group of dogs with different ancestry will be healthier than their purebred counterparts. Heterosis is a theory in which the phenomenon of crossing two consanguineous lines (inbreeding) can produce descendants with better genetic base. In addition to the lack of genetic suppressing present in general in the inbred crosses and purebred dogs there is a remote effect of inbreeding in any breed. Heterosis is also conditioned by superdominance, i.e. the best combination of functions of two different genes (alleles) in the gene location (locus) in comparison with the same combination of two identical alleles. Better health and vigor will not create a superior breed, but the benefits derived from it, are the factors, producing the extra hybrid energy or power. After all, the main purpose is not to create a new breed, but to create a healthy and happy animal. Heterosis effect gives a strong, vigorous dog with a reduced level of genetic diseases. In livestock breeding is well known that hybrids (crossed 50% to 50% of two different species) have fewer genetic diseases, as any detrimental effect doubling will stop in the first generation. The genetic term for this phenomenon is the effect of heterosis. This effect is often endowed unrelated individuals with more powerful descendants than inbreeds may do.
The goal of breeders, engaged in hybrids breeding is to obtain healthy and happy dogs without any genetic problems.
For example, breeders crossing with a poodle are in a search for soft, silky and nonmolting coat, better for the highly allergic individuals.
Purpose of these hybrids is not necessary to create a new breed.
As when crossing of two purebreds goes beyond the first generation, heterosis effect may lost. But to obtain this effect is the goal of most hybrid breeders.
Dog female must always be bigger in size, for puppies would not be too big to cause any complications during delivery. Heterosis, as said, is not necessarily occurred in the first generation coupling of unrelated hybrids of the same (or other) type will also give a similar effect although it will affect the offspring in different ways.
When crossing two different types of purebred dogs you can get combination of any features found in each breed. If you prefer hybrids how would you determine which mix to choose? Read about temperament and care rules for both species to be ready for any combination of both traits.
If everything about these breeds fits you and your lifestyle, then you can most likely assume this cross is developed for you. If there are FACTORS about either breed in the cross for which you do not feel any disposition better to avoid this cross.
It is also important to be aware that none of these designer hybrids are crossed 50/50 percent of purebreds. It is normal for breeders to produce multi-generation crosses. For instance, a simple cross of F1 generation gives the maximum hybrid vigor in the dog, then the deeper we follow the chain of different generations, the more vigor will be lost in the hybrid, but there are some advantages in several generations crossing. If you want to enhance your chances of getting certain traits, such as non-shedding, you have to move on down the chain of generations, risking less heterosis effect.
To help to understand this concept we will use the Labradoodle breed as an example. Labradoodle is a cross between the Labrador Retriever and the Poodle (usually standard size Poodle). In general, we will call the first breed as "purebred-A" and the second as "purebred-B". Note: examples of the coat differences apply only to the Labradoodle breed cross; all other hybrids will vary each in its own way, depending on which breeds present in that cross.
F1 = puppy of the first generation - 50% of purebred-A and 50% of purebred-B. For example, a mixture of a Labrador Retriever to Poodle in the first generation produces healthier progeny. In this particular Labradoodle cross, type of coat can be smooth like Retriever’s, hard as the Irish wolfhound’s, or curly / shaggy like a Poodle’s coat. It can shed or to be non-shedding and puppies in the same litter may strongly differ from each other. This is not the best option for people with allergies.
F1b = puppy with backcrossing - (crossing of the first generation hybrid with one of its parents) with 25% of purebred-A and 75% of purebred-B specimens.
For example, a cross between F1 Labradoodle back to Poodle; it is a Labradoodle bred back to Poodle - Doodle with wavy, curly hair, shaggy in appearance, is one of the individuals with very consistent type of coat.
Crossbreed F1b is more likely a Doodle with nonmolting hypoallergenic coat most unpretentious in care.
F2 = puppy of a second generation - hybrid F1, mixed with a hybrid F1. For instance, Labradoodle F1 crossed with Labradoodle F1. In such combination, you will get the same share of purebred-A and purebred-B, as if it would be a hybrid F1. But in this case Labradoodle will likely shed.
F2b = second generation puppy with F1 backcrossing, where F1b is crossed with F1.
F3 is a hybrid F2 to hybrid F2. F3 = F2 x F2.
Multi-generation = F3 or hybrids of earlier generations (F1, F2), crossed with F3 or earlier hybrids.
Purebred-A x purebred-B = Hybrid Dog F1
F1 x Purebred-A = Hybrid dog F1b (with backcrossing)
F1 x F1 = Dog Hybrid F2
F1 x F1b = Dog Hybrid F2b
F2 x F2 = Hybrid dog F3
And remember, hybrids breeding may not produce the result you expected.
For example, creating a cross between a Golden Retriever and a Poodle (Goldendoodle) you can or cannot get a dog that sheds.
Most seasoned breeders can tell you what characteristics will develop in the dog as it grows up. For example, for Goldendoodle some breeders can tell what type of hair your puppy will have from the Retriever or from Poodle although it is still hard to give an unambiguous guarantee. It is often difficult to determine what type of temperament each puppy will have, as some characteristics will show up only during older age, which comes after adoption to the family.