Thanks for input Fred.
So let me get this straight. There is some sort of "standard" to judge what a pure breed is and what is hybrid?
Yes, of course. The American Poultry Association establishes the standard for each breed and publishes them in the Book, The Standard of Perfection. The book is the bible of breeds. There is an inexpensive version for around $70 and a nice, hard bound for around $120
If a bird is not a good specimen of that breed then it is not considered part of that breed, but is considered a hybrid? But that does not make sense. Because, for example all leghorns are considered leghorns no matter how bad a leghorn it is, if it's parents are leghorns it is a leghorn. I'm still not getting it.
Not quite. Again, as I said earlier, the word hybrid suggests intentionality. An intentional cross to purposely create a bird. There are reasons, which might include easy to sex at hatch (sex link) improved meat (meat bird crosses) and so forth.
The easiest thing to remember is this. 95% of all the chickens in the world are chickens. Just chickens. The laying industry uses billions of high laying hybrids, mixes and crosses and the meat industry uses billions of the meat bird crosses and hybrids for meat production. None of these birds are a breed of any kind. The vast majority of barn yard birds, barn yard mixes/mutts are also not any particular breed either. No one cares. They are often good chickens.
Sure, if Leghorns lay fertile eggs a Leghorn chick will hatch. But, chickens are not like AKC registered dogs, or Registered Angus cattle. These are mammals and the sense of being purebred stems from the purity of the parents and the purity of the parents on backward. This is called a registry of pedigree. Nothing like this is kept for chickens.
Chickens are therefor not genotype (pedigree by genes) but phenotype (what does it look like). This is why the term purebred may be used in common speech, but it isn't what is used in the poultry world. Truebred is more accurate when talking chickens. Does the bird in front of you LOOK like the Standard laid out for the bird? How close to being a "perfect" example of the breed is this bird? That's the question that is asked, Chicken people do not ask, "Is it purebred?" They look with knowledgeable eyes and must judge whether it meets the Standards. That's the right question. Is this bird in front me a so-so Leghorn? A very good Leghorn, or a very poor Leghorn. Each bird is judged on its own merits.
And besides, what would this standard mean in practical terms? Are hybrids not as good quality birds for their meat or eggs? (is that why they are a bit cheaper). What if a hybrid was crossed with another hybrid(a goldline x goldline for example)? What would you get, the same hybrid offspring (goldline in this case)? And why do I hardly ever see hybrid roosters? Where have all the hybrid roosters dissapeared to? What's a hybrid hen supposed to do when it can't find any hybrid roosters?