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Name: Steve
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Can mammals of different species interbreed. Obviously certain physical charteristics would prevent this. But, is it possible for example for a cow and a horse to mate and have offspring. If its not possible ....why????

The classical example of interspecies breeding is ofcourse the mule, from a horse and a donkey. Other examples are tigers breeding with lions to produce 'ligers', and sheep with goats. In all of these cases the species are close enough to allow breeding, but the offspring is sterile (I am sure about the mule,not about the others). Other than behavioural difficulties (do they understand each others 'courting' language?) there are important biolgogical restrictions at the DNA level for interspecies breeding. The chromosomes of the sperm and egg cell have to match sufficiently to start deviding. So the two species must be genetically close enough. Beside genes the DNA contains many repeated sequences, that have not meaning as far as we know, and these seem to be involved in determining the genetic match. There is still a lot of research done in this area.

Dr. Wassenaar

There are sooo many barriers and considerations to realize.

Behavior differences (different species do not have the same behaviors required to creating the mating behaviors. Physical (structural) differences ( the mating apparatus must be compatible to both sexes.

Chromosome number differences (This is the key! They have to pair up to operate and if you are dealing with different numbers or different traits in the same location, NOTHING will develop!

Internal chemistry differences ( timing of mating season, timing of fertilization, chemistry needed to penetrate the egg, etc.

Sperm enzyme differences (similar to above for the sperm must have the right enzymes to penetrate the egg to fertilize.

Chemical signaling differences (This is complex but it is essential the Internal Chemistry differences)

Immune system differences in response to foreign bodies (sperm is a foreign body).

These are just off the top of my head. All of these are significant in a big way.

Steve Sample

The strict definition of species is NO. But there are noted exceptions. It depends how far separated in evolution the species are. It is believed that all dogs descended from a wolf-like species and dogs and wolves have been known to interbreed. Usually though, even if two different species interbreed and produce offspring, THEIR offspring cannot produce offspring. An example is the mating of a horse and a donkey. The outcome is a mule and mules are sterile. The only way to get more mules is to mate horses and donkeys again. One of the barriers seems to be that different species have different numbers of chromosomes and they would not pair up evenly at meiosis. So for example chimps and humans are very close together in the amount of DNA, but chimps have 48 chromosomes and humans have 46.

Van Hoeck

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