Can any one tell me why breeding between species is not possible?

Answer 1

Here are 8 reasons called reproductive constraints that will not allow the production of a fertile offspring between 2 different species. These factors can be classified as prezygotic (constraint that makes mating difficult) and postzygotic (constraint that prevents a zygote from developing).

Prezygotic Constraints:

1. Habitat Isolation. Two species may live in the same area but in different habitats. Living in these different habitats ( in water, living on land, or living in tree tops) effectively segregate these organisms from each other. Since there is little if any contact the possibility of successfully mating is drastically reduced.

2. Temporal Isolation. Two species that breed at different times of the day, season, or year cannot mix their gametes. Since the breeding times are different there is no chance of reproductive contact.

3. Behavioral Isolation. Species-specific signals and elaborate behavioral patterns are used by closely related species to insure contact with the proper mate. Birds, mammals, and insects have pre-mating rituals that attract the proper mate. These signals can be chemical or physical in nature. Other organisms pay little or no attention to these behaviors or scents.

4. Mechanical Isolation. Anatomical incompatibility may prevent sperm transfer between two closely related species. The absence of certain appendages or their modification may inhibit a male from grasping and successfully fertilizing the female. Difference in floral structure may prevent pollen from reaching the stigma of the intended flower.

5. Gametic Isolation. If for some reason foreign sperm is introduced into a female there are several preventative measures to insure that there is no union between the sperm and egg. Internal environmental conditions may cause the sperm to die. Gamete recognition sites on the sperm do not fit with the intended egg. If the two species differ in the type of fertilization (external and internal) there is no chance of the sperm ever contacting the egg.

Postzygotic Constraints: If prezygotic constraints are crossed and a hybrid zygote forms, one of several constraints will prevent development of a viable, fertile hybrid.

1. Reduced Hybrid Viability. Genetic incompatibilities between the species may abort the development of the hybrid during some stage of development. Difference in chromosome number may cause abnormal cell division. Since the chromosomes align to insure equal distribution upon cytokinesis, abnormal chromosome counts could occur based on this numerical difference.

2. Reduced Hybrid Fertility. If two species mate and produce a viable offspring, these offspring will be sterile due to the misalignment of the chromosome number. During gametogenesis the odd number of chromosomes makes it impossible for viable gametes to be produced by meiosis.

3. Hybrid Breakdown. In some cases a fertile hybrid is produced. When these hybrids mate with each other, their offspring of the next generation are feeble or sterile.

Answer 2

So much knowledge, and so much wrong. There are quite a number of species that can interbreed and produce offspring; some of those are even able to produce fertile or selectively fertile offspring. "Species" is a fairly arbitrary term, that generally means a population that enjoys reproductive isolation from related populations. This may be because it lives in a different area, or it has breeding behaviors that identify it as different, from related or similar species. That in no way means that separate species _can't_ interbreed; just that in the wild, they generally _don't_ interbreed. Hybrids do occur naturally, but usually only rarely. And wolves and dogs in fact are separate species. There are several separate species of wolves, and only one species of dog (which has a whole bunch of races or whatever term you wish to use for the various 'breeds'). Remember - just because someone says something, that doesn't make it so; always check, and be skeptical!
Incidentally, ATP-man's answer is good, but it's not complete.

Answer 3

That is speculation, not proof. No one was there to observe it. Nor can it be demonstrated. Evolutionists believe that, if given enough time, random or chance mutations in the genetic code caused by random environmental forces such as radiation will produce entirely new genes for entirely new traits which natural selection can act upon or preserve. However, there is no scientific evidence whatsoever that random mutations have the ability to generate entirely new genes which would program for the development of entirely new traits in species. It would require genetic engineering to accomplish such a feat. Random genetic mutations caused by the environment will never qualify as genetic engineering! Mutations are accidents in the sequential molecular structure of the genetic code and they are almost always harmful, as would be expected from accidents. Of course, just like some earthquakes that don't do any damage to buildings, there are also mutations that don't do any biological harm. But, even if a good mutation does occur for every good mutation there will be hundreds of harmful ones with the net result over time being disastrous for the species. Furthermore, only those mutations produced in the genes of reproductive cells, such as sperm in the male and ovum (or egg cell) in the female, are passed on to offspring. Mutations and any changes produced in other body cells are not transmitted. For example, if a woman were to lose a finger it would not result in her baby being born with a missing finger. Similarly, even if an ape ever learned to walk upright, it could not pass this characteristic on to its descendants. Thus, modern biology has disproved the once-held theory that acquired characteristics from the environment can be transmitted into the genetic code of offspring. Most biological variations within a biological kind (i.e. varieties of humans, dogs, cats, horses, mice, etc.) are the result of new combinations of already existing genes and not because of mutations.

Answer 4

because the definition of species is something that can't breed... There are very few cases of animals being able to breed within species (and the result is sterile offspring).

Ok, so why can't two different species breed? Because they have different numbers of chromosomes, different DNA sequences, different mating habits, etc.

Answer 5

Because of semantic.
If two separate organisms can breed successfully (which means they would produce viable offspring wich in turn can also mate and breed successfully and so on) They are members of the same species

Answer 6

This is because of our chromosomes or genes. We have a certain amount and they fit perfectly and only with another set of human genes. The same with a dog can only go with a dog because its chromosomes only match up with its own species. This also though could be crossbreed with a wolf but they are similar and are in the same family

Answer 7

Guitar Guy has the simplest correct explanation. Except for the part about wolves and dogs. They can interbreed because they are actually the same species. They only look different on the surface.

Answer 8

Because Speciation means that the the gene sequences for both zygotes can't be mixed because the sequences for the DNA bases are to far off to pair up correctly.

Answer 9

it is possible by cross breeding

Answer 10

becoz individuals from two different species are sexually incompatible with each other.