# Ratmice Micerats Mules



## Howard (Apr 26, 2009)

I am asking a hypothetical question. Is it theoretically within the bounds of possibility, even remotely, that a mouse/rat mule could be produced; or are they too distantly related? I am disregarding the likelihood of the rat killing the mouse, or any other such practicalities. (_I am not contemplating attempting the idea even for a moment). _I am just interested in the hypothesis.


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## moustress (Sep 25, 2009)

That would be a big 'no', I'm pretty sure. The body chemistry is different enough, to start with, and I don't think they have the same number of chromosomes. It's a fun idea, though; like a shortcut to producing really, really, really big mousies!


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## Jack Garcia (Oct 9, 2009)

Rats have 42 chromosomes; mice have 40. That in and of itself does not stop hybridization, though, as there are animal hybrids with parents of different chromosomal counts.

However, mice and rats are not only different species but also different genera, and that doesn't prevent hybridization except in very rare cases.

Besides, as you noted, the rats would make dinner out of the mice. 

With all that said, there are examples of scientists taking rat genes and implanting them into mouse embryos (such as the rat growth hormone gene). But these are not true "hybrids," don't occur naturally, and I would assume never make it outside the laboratory as most lab mice are destroyed after they've been used for their intended purposes, as far as I know.


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## Autumn2005 (Apr 21, 2010)

Horses have 64 chromosomes, donkies 62, which creates mule and hennies with 63 chromosomes, which is why they're sterile. What if there was a really small rat and a large show mouse?


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## Wight Isle Stud (May 19, 2010)

Gonna have to say, I had mice 12" long, and you could get a pound coin sat between their ears, I can produce photographs, but it is a fact. It is amazing what can be produced. Fix it then select for other features. These are the mice from the past, I have bred them. they say that mice are not the same as they used to be, quite frankly they are not. How do we get back to that /the answer is to have the specialist studs that we had in the past, i.e. dek Taylor with 200 selfs of one breed, or frank hawley with 60 boxes of cream satins, when he got fed upof this he bred dutch- LOL i can remember their size !- and the champions he registered.


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## Jack Garcia (Oct 9, 2009)

I'll be back. said:


> Gonna have to say, I had mice 12" long, and you could get a pound coin sat between their ears, I can produce photographs, but it is a fact. It is amazing what can be produced. Fix it then select for other features. These are the mice from the past, I have bred them. they say that mice are not the same as they used to be, quite frankly they are not. How do we get back to that /the answer is to have the specialist studs that we had in the past, i.e. dek Taylor with 200 selfs of one breed, or frank hawley with 60 boxes of cream satins, when he got fed upof this he bred dutch- LOL i can remember their size !- and the champions he registered.


This is very true. I long for the days (although I never lived in them) when people bred mice responsibly and stuck to one or two varieties at most. I have had some silvers and champagnes who were over 12", but not many. A lot of mine seem to "top out" at just under 12".


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## Rhasputin (Feb 21, 2010)

Hamster/mouse hybrids exist, so however un-likely, I wouldn't be surprised if someone somehow made a rat-mouse!


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## Jack Garcia (Oct 9, 2009)

They do not.


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## Rhasputin (Feb 21, 2010)

They do so!

EDIT: Well, let me be more specific. You can't breed a hamster and a mouse, and get hybrid babies. There is a lot of science involved. You can also have transgenic animals, where they carry genes from other animals, which has been done with ratsXmice.


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## Jack Garcia (Oct 9, 2009)

Where's your evidence?

Cell lines exist, but cell lines do not a hybrid animal make.


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## Rhasputin (Feb 21, 2010)

Quote from Ratbehavior.org:

"Rats and mice are not that closely related. Under normal circumstances, rats and mice are not attracted to each other and will not mate. Even if the sperm of one and the eggs of the other are mixed together artificially, fertilization will not occur: the eggs of one do not allow entry of the other's sperm.

These natural barriers can be overcome in a laboratory, at least at first. Such attempts typically result in a hybrid embryo which dies after a few cell divisions.

For example, the egg's protective covering can be stripped off, allowing the sperm of the other species access to the egg. Sperm can also be injected directly into the egg. When this is done, fertilization occurs. The resulting hybrid embryo is not viable, however. It typically goes through one cell division, resulting in a two-cell embryo, then it degenerates.

Another technique involves removing the nucleus (which contains most of the DNA) from a mouse egg and replacing it with a rat's nucleus. The resulting embryo has 100% rat nuclear DNA, enclosed in a mouse egg with mouse cell contents (cytoplasm). These nuclear transplant hybrids sometimes live to the 2-cell stage, but then they degenerate. The rat nucleus and the mouse cytoplasm are fundamentally incompatible.

Early stage embryos can also be merged, creating chimeras. Early stage embryos are just tiny clusters of a few undifferentiated cells. Chimeras are typically created by combining two early-stage embryos, producing a single merged embryo. The resulting individual is made up of two populations of cells, each descended from one of two fertilized ova. Chimeras have been attempted between species, including rats and mice. These were created by merging early stage rat and mouse embryos. The resulting chimeras developed normally in vitro, but when they were inserted into a hormonally primed host they were lost during or shortly after implantation.

In one case, however, using a different technique, a few of the chimeric rat-mouse embryos implanted successfully. They developed normally in vivo for about a week, before being removed and examined. The researchers found that the mouse cells gained the advantage: the mouse cells came to dominate the embryo and rat cells became rare.

Secondary chimeras are created when cells, organs, or tissue from one species are implanted into another. This procedure (called xenografting), is frequently and successfully performed in laboratories. For example, rat bone marrow can be injected into an immunosuppressed mouse, where it takes hold and produces white blood cells. Or a piece of rat skin could be grafted onto an immunosuppressed mouse. These mice with rat-tissue transplants have cells from both species, and therefore fit the definition of a chimera, but they are technically not hybrids.

Two additional techniques deserve mention: the creation of transgenic rats and rat-mouse hybrid cell lines.

Transgenic rats are rats that carry a gene from another species. The foreign gene is inserted into the fertilized rat egg, and the resulting rat carries the new gene in every one of its cells. Many types of transgenic animals have been produced, including rats that carry a mouse gene. The genome of these transgenic rats is almost 100% rat, of course, as they only have one or a few genes from other species.

Lastly, hybrid cell lines can be created in laboratories by fusing cells from two species and maintaining the resulting merged cells in a culture medium. Many such hybrid cell lines have been created, including rat-mouse hybrid cell lines. These cells will not, however, grow up to be a whole hybrid organism."


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## Rhasputin (Feb 21, 2010)

I'm using hybrid in a broad sense, too. :roll:


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## Jack Garcia (Oct 9, 2009)

Do you have permission to quote that? The owner is really protective of the material on the site.

Besides, nothing you have posted says hamster/mouse or rat/mouse hybrids exist. They're speaking of cell lines and gene transplants in the lab. These exist, but are not hybrid animals in the way that people speak of them (such as a mule).


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## Jack Garcia (Oct 9, 2009)

Think of it this way. Using your logic ("hybrid in a broad sense"), there would be said to exist human/mouse hybrids, jellyfish/firefly hybrids, and so forth. That's not a correct use of "hybrid" and is not what Howard was asking about, though it is interesting.

You're confusing "hybrid" (two separate species producing offspring, which usually occurs naturally) with "transgenic" (carrying the genes of another species, created in a lab).

Edit: here is an interesting appraisal: http://www.actionbioscience.org/biotech/margawati.html


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## Rhasputin (Feb 21, 2010)

Like I said. Hybrid in a broad sense, meaning 'one thing made of two different things' I guess. You can't put a mouse and rat together, and get babies. Period. 
I'm just saying it's possible to put parts together and end up with something somewhere in between. Even if something created is 99.9% of one animal, and .1% another animal, it's still two animals put together.

I understand that it's not a hybrid like a mule or a liger or something. 

Hybrid: Something of mixed origin or composition
That is how I'm using it I suppose.

If it bothers you that I quoted it, then I'll just change it to a link.


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## Jack Garcia (Oct 9, 2009)

It doesn't bother me. I know Ann has asked people not to do it before, though.

_Hybrid_, when talking about animals, is used in the original, biological sense.


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## Rhasputin (Feb 21, 2010)

Okay then, how about: It's possible to create a _composite_ animal? :lol:

(I'll ask about it, and if it's a problem, I'll take down the quote, and just leave a link.  )


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## Jack Garcia (Oct 9, 2009)

Haha. It bothers me so much when people invent new, one-person terms to cover scientific/biological phenomena which already have established meanings and precise definitions, especially when one of our most important tasks as mouse fanciers is to educate the public. Being as clear and as thoughtful as possible about our choice of words is _always_ a good thing. I've said this before and I know I'm a stickler for this point. But the holiday weekend is upon me and I need to get going, so alas, I digress!


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## moustress (Sep 25, 2009)

We are all swimming in a very small pond; on top of that there's no money to be made in being a mousekeeper, so I doubt the issue would ever arise. Very few scientists, I am sure are afraid of usn's taking off with their info or claiming it as our own. which, as far as I can tell, no one is doing.


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