What's the difference between a "breed" and a "hybrid" in chicken taxonomy?

[Oldhound]

Just a few cents from an old ( retired) dog man. We were all taught that a Horse bred to a donkey produced a Hybrid , a mule, which for all intents and purposes is sterile.
In the world of agriculture the word Hybrid is used in the place of crossbreeding . Be it hogs, chickens, vegetables, and so forth, Hybrid is applied to crossbreds that do not reproduce themselves when bred together.
Oh yes the color genetics in chickens is so much more complicated than dogs or any other animal with hair. Dogs , cats, horses etc are a breeze to understand , chickens Not so much. There is a FB group discussing the color genetics of chickens that helps but it has not been easy for me to wrap my mind around it. Just to complicate my life more I recently acquired Fibro Melanistic birds and will be playing with that factor. I have found that as it did with dogs, a knowledgeable mentor is invaluable. Bill

 

[tadkerson]

The biological taxonomy of the common chicken is Gallus gallus domesticus. In other words, this would mean that any "breed" of chicken, whether it's a leghorn or a silkie or whatever, is exactly the same genus, species and subspecies as any other. So, a "breed" of chicken, then, is nothing more than a group of Gallus gallus domesticus that displays a certain homogenous physical appearance and has a set of homogenous characteristics that go along with that homogenous appearance. Supposedly, all common chickens descended from and are a subspecies of the red junglefowl (Gallus gallus) and the different "breeds" have been achieved over the last 6000 or 8000 years of domestication through selective breeding to single out specific physical and/or behavioral characteristics, much in the same way as all of the different breeds of dogs make up a single subspecies (Canis lupus familiaris) of their common ancestor, Canis lupus.

OK....so what then is a "hybrid" chicken? I have seen some websites claim that a "hybrid" chicken is nothing more than a cross between two "breeds"? But two different "breeds" of chickens still belong to the very same subspecies. And a hybrid, at least from a biological taxonomy perspective, is an offspring resulting from the cross between two different species of animals. Now maybe lay chicken taxonomy is different than biological taxonomy and these websites are correct, and I'm OK with that.....but, the way we continue to make more "breeds" is by crossing existing "breeds", so why would we ever refer to any crosses at all as hybrids? With this type of taxonomical system, how would one ever truly distinguish a "breed" from a "hybrid" in the chicken world? I would expect that the results of any cross between two different "breeds" which didn't exhibit any obvious common set of homogenous characteristics would simply be referred to as a "mixed breed" or something equivalent to the "mutt" in the dog breeder's world.

The reason I'm curious about this is because I have read that some chicken "breeds" have better fertility rates than others. Inbreeding can surely explain this, but if the same good husbandry standards and practices have been used for the development of all "breeds" to keep inbreeding to a minimum, one would think that all "breeds" would have about the same fertility rate (unless, of course, infertility is simply a homogenous genetic characteristic that runs parallel to certain homogenous physical appearance characteristics, and this is certainly possible). But, assuming the former to be true, then true hybridization (the crossing of two similar but different species) present in the history of some "breeds" could account for infertility rates to be different between different "breeds".

To confuse matters worse, some people believe that Gallus gallus domesticus, the common chicken, is an ancient hybrid cross between red junglefowl (Gallus gallus) and gray junglefowl (Gallus sonneratii). This would mean that all common chickens, regardless of "breed", would be true hybrids. But, whether or not there was hybridization between G. gallus and G. sonneratii early on in the development of Gallus gallus domesticus, is it possible that the development of more recent "breeds" (say, within the last 1000 years) are the result of some hybridization between Gallus gallus domesticus and another species within the genus Gallus? If so, this would mean that some "breeds" are not Gallus gallus domesticus and some are.

Any thoughts on any of this? This is a subject that, as an unschooled backyard biologist/zoologist (I'm a degreed technologist with a passion for natural sciences), is of great interest to me.

Do not confuse taxonomic terminology with genetic terminology. If an individual crosses two organisms within the same genus, the offspring is a hybrid (taxonomic). Or two morphological individuals within the same species.

Genetics is different- crossing two chickens with different alleles ( at one locus) produces hybrid offspring. Crossing a barred leghorn with a dominant white leghorn produces offspring that are hybrids or heterozygous at the dominant white locus. The offspring carry a dominant white allele and a recessive non-dominant white allele. Purebred or homozygous individuals are genetically the same; the two individuals carry the exact same genes.

Monohybrid - one locus

dihybrid- two loci

trihybrid- three loci etc.

Tim

 

[Rosa moschata]

The term "hybrid" denotes a cross between two "types", and "types" can mean species, subspecies, races, breeds, or even down to a single trait. The idea is that at the level at which the discussion is concerned, "pure" refers to individuals of the same "type" which, if bred together, will have offspring of the same "type" (again, with respect to the level of "type" being discussed). A "hybrid" is the offspring of two different "types". Taxonomy deals with "types" as species or subspecies as the (generally) basic level. Genetics looks at individual traits (which may differ because of one genetic difference, more than one, or a suite which show degrees of expression, etc.) In chickens (and other domesticated animals and plants), the basic level can be "breed" (a group maintaining a shared general appearance, superficially similar to a species, but the result of exaggerating strongly-expressive individual traits), or like in genetics, with respect to specific traits within a breed (such as crossing a black and a self-blue of the same breed -- the offspring would be black hybrids heterozygous for self-blue).

In taxonomy, a hybrid would refer to a cross between two species most often, sometimes also between subspecies of the same species. Offspring typically look like something in-between their parents, and if they are also fertile and allowed to breed among themselves, offspring will show varying degrees of each original parent species -- thus, they won't "breed true" to either species with regards to physical characteristics.

In genetics, a hybrid refers to a cross between two different homozygous traits, or between two pure-breeding strains. One example would be the foundation of genetics, the studies of Gregor Mendel. He crossed different pure strains of peas, and the offspring were hybrids -- same species, different "types" with respect to specific traits (green versus yellow pea color, wrinkled versus smooth pea texture, tall versus short pea plant, etc). Since peas tend to self-fertilize without interference, hybridizing required manual transfer of pollen from one to another which had been emasculated. The offspring, if left to self-fertilize, would then beget offspring which were not all the same with respect to the specific traits observed -- thus the crossed peas would be called "hybrids" because they wouldn't "breed true".

In chickens (and also in many plants raised from seeds), buying hybrids means that the individuals had parents of two different "types" -- breeds in the case of chickens, or inbred strains in the case of seeds. The first-generation cross results in a general uniformity among the offspring, to the extent that you might think they were a pure breed or strain. But if they were left to breed among themselves, their offspring would be variable. And hence the term "hybrid" -- they don't breed true. The reason the first-generation hybrids are so generally uniform is because of a balancing of homozygous dominant and recessive traits from the different pure parent-breeds into straight heterozygosity in the hybrid offspring. They're uniform enough that one might think they actually are a "breed". But because the first-generation hybrids (F1) are heterozygous, the individual traits would segregate in new combinations in the second-generation hybrids (F2) non-uniformly. If you want to create a pure-breeding new type of chicken combining traits of two (or more) different parent breeds, you'd have to keep breeding the hybrids together until you 1) find what you want, and 2) get them to the point that all their offspring ALSO have what you want. In effect, you are making a new combination of homozygosity for the traits you desire. Until then, chickens with mixed ancestry that are very variable between their siblings are not generally called hybrids -- they're "mutts" or "mixed-breeds".

The point is that the term is used to represent crossing two different types. What that type is will depend on the context of discussion.