Human-Mouse Hybrids? 433
scientistguy writes "There is a remarkable story by Nicholas Wade in the early
morning edition of the New York Times about a discussion to create human-mouse
hybrid organisms. One of these techniques involves the introduction of genetically altered mouse embryonic stem (ES) cells (e.g. with
genes 'knocked-out' or replaced) into a developing mouse blactocyst to create progeny hybrid organisms. Typically, these progeny organisms are then bred to unaltered mice to see
if the genetic alteration has gone germline or is heritable. If heritable, mice can be bred and
animals which are homozygous for the altered gene can be phenotypically examined as long as the manipulation is not homozygous lethal or cause
sterility in a single copy state. Unless using
blastocysts from immunologically crippled mice, there would most likely be a recognition of non-self by murine immune cells not educated (which haven't seen during their development) to the human cells that would wipe them out. Nonetheless, it's amazing that it's
being contemplated due to the ethical implications of such an experiment. What if it were viable? What if there were more than just a few
human cells? Could it be sacrificed? ... or even experimented on further if part 'human'? Perhaps these
types of experiments are best relegated to little known, deserted islands far
away from the reaches of civilization (or perhaps regulation) ..."
Where...? (Score:5, Funny)
What - like Australia ?
Re:Where...? (Score:5, Insightful)
These kind of moves are actually dangerous. If the civilized world chooses to ban something of some reason (hopefully a good one), one can just go to a poor country and be fully legal.
We recently saw this when an oil tanker collapsed just off the coast of Spain. The tanker was registerd in Bermuda (or somewhere around there). Thus it was sheaper taxwise, less regulated working-environment and safety wise and could therefore go to sea without being sea worthy.
We can also see this in the research of the (somewhat) mad Italian sientist, Dr. Severino Antinori. He claims to creating the first cloned human and that it is going to be born early next year. He refuses to say where the experiment has been made, but it is in a country with weaker legalization than most western contries.
To sum things up. This type of experiments will probably have to go to some little known, desterd island, but I regret that they can.
Re:Where...? (Score:3, Informative)
The nation of registry of choice for many ships is currently Liberia. Just think about it the next time you consider going on one of those delightful Disney cruises.
Re:Where...? (Score:2, Informative)
Some reason (hopefully a good one) (Score:5, Insightful)
Also, moving services and "dirty" plants to unregulated countries and the subsequent pressure (mostly economic but sometimes even military) to keep these countries unregulated is caused mainly by the major corporations of "civilized" Western countries, not by mad scientists or WTO eco-freaks. You should ask yourself who is served by a cheaper oil tanker (or a cheaper Nike produce by Vietnamese semi-slaves).
Two points... (Score:3, Insightful)
An instance of "civilized" country has been recently letting the religious right decide what can and what can not be researched. Steem-cell and cloning studies are being banned because some religious texts were interpreted as saying that this sort of thing is "unholy".
Which is having the effect of a ban (Score:3, Interesting)
Bush's extremely restrictive funding guidelines not only had the practicle effect of stopping the research in the US, but also sent a strong message to investors: the Religious Right has the power to severely restrict this technology, despite the claims of scientists that it might lead to cures for some of the biggest killers of humankind.
In such a climate, very little venture funding is being released, after all it's one thing to bet whether a new technology will work out or not, it's quite another thing to bet whether you will lose your money because Falwell decides your technology is immoral...
The reference... (Score:2, Informative)
Jeez (Score:2, Interesting)
Sounds like a good movie (Score:2, Funny)
Re:Sounds like a good movie (Score:2)
his "Ben" them again since it calmed the killer
mice down before.
wow (Score:3, Funny)
Why not just stick my mouse to my hand with superglue?
What are we going to do tonight Brain? (Score:3, Funny)
Re:What are we going to do tonight Brain? (Score:2, Funny)
(and that is, of course, Brain's problem. Had he listened to another animated short fellow with a big head, he would know: "Do. Or Do Not. There Is No Try.")
Registration Free Link (Score:5, Informative)
Cheers Google ...
Woo Hoo! (Score:2, Funny)
Ehhhhhh (Score:5, Funny)
Good god! Don't you understand the implications though? If the digital tri-mode defrobulator gets out of sync with the anticalisthenticator, we could have some serious subdermal anamolous activity!
Open your eyes man!
(I just thought the sentence sounded funny the way it was strung together, even if I do have enough biology to know what a blastocyst is and to recognize when it's misspelled)
Are you a man or a mouse ? (Score:5, Funny)
Oh very freaking funny you insensitive clod!
I'm horrified... (Score:4, Interesting)
He gave as an extreme example the possibility that a mouse making human sperm might accidentally be allowed to mate with a mouse that had made its eggs from human cells. He gave as an extreme example the possibility that a mouse making human sperm might accidentally be allowed to mate with a mouse that had made its eggs from human cells.
Re:I'm horrified... (Score:2)
Na na na na na na MOUSE MAN! MOUSE MAN! MOUSE MAN!
Quickly Sparrow, to the Mouse Cave!
Re:I'm horrified... (Score:4, Funny)
That's pretty brave. I'm just an organ donor myself.
Re:I'm horrified... (Score:2)
I consider myself open to scientific experimentation
So, you must eat at taco bell.
Re:I'm horrified... (Score:4, Informative)
Also, the Bishop's comment about a few human cells per organ being acceptable: not the way it works. As I said, there will be NO human cells, and the modified cells will come in patches. As a modified cell in the blastocyte divides, all it's progeny will have the modifications, so you'll end up with an area in the adult organism that has the modifications. Is it really too much to ask that the people who are trying to make these ethical decisions put in the effort to actually learn what they're talking about before passing judgment?
Re:I'm horrified... (Score:2)
Re:I'm horrified... (Score:2, Interesting)
I do understand and, to a certain degree, share your concerns. This is a whole new realm of investigation, and scientific enthusiasm must be tempered by ethical considerations. But for those considerations to be relevant, they must be based on facts. The reporter had most of his facts wrong, and the Bishop's grasp of what the scientists were doing was even worse. The techniques the scientists are using are on fairly firm ethical ground, it's just the very poor reporting job in the article that makes them sound scary.
Re:I'm horrified... (Score:3, Funny)
He gave as an extreme example the possibility that a mouse making human sperm might accidentally be allowed to mate with a mouse that had made its eggs from human cells.
Hey baby, I'd like you to my parents, Squeeky and Whiskers.
Re:I'm horrified... (sperm/egg combo in a mouse?) (Score:2)
For organisms with such tiny heads, spermatazoa are pretty good at what they do. They swim, and swim, and swim, and swim--until they die, or smack into an ovum. They'd probably have a better shot inside a mouse uterus than a human one, just because there's a smaller volume to traverse while hunting for an egg. (Granted, mice deliver less ejaculate than humans.)
And yes, 'really small tweezers' is actually pretty close to the technique currently used for in vitro fertilization.
Re:I'm horrified... (sperm/egg combo in a mouse?) (Score:2, Funny)
Have a heart (Score:3, Funny)
Mental images (Score:2, Funny)
So potentially, (Score:5, Funny)
1000 genetically altered monkees 10 years to create
the collective works of shakespeare. You probably
wouldn't have to lock them in a room either. They'd
of course be superior and have 3 asses.
Re:So potentially, (Score:2)
Three? Between the 1000 of them?
Mickey Mo---human! (Score:2)
I'll name him Mickey out of spite of Disney.
But instead of Pluto, I will give him a four-assed monkey for a pet, as an homage to South Park.
Re:Mickey Mo---human! (Score:2)
*sighs*
When will humankind ever learn and stick to its simple, one-ass schematics?
Hardware vs. software (Score:5, Interesting)
Human-mouse hybrids? So what. Within a generation you will be able to design any lifeform you can imagine on your computer screen, and 'print' it into a virgin cell that will grow into your animal or plant.
It is an inevitable progression. DNA is a digital code, and it is just a matter of horsepower to crack and then manipulate it.
Re:Hardware vs. software (Score:2)
Re:Hardware vs. software (Score:2)
In other words, any solvable problem, no matter how complex, will be solved.
Is digital life solvable? That is the question.
If the answer is 'yes' (and all signs are that this it is) then it is inevitable that we will eventually make it as common-place as all the other 'magical' technologies that we use today.
Re:Hardware vs. software (Score:2)
Humans exploit the cognitive niche
and this means that we push forward.
There is no inevitability in our progress
nor even in our presence, but short-term
predictions are quite safe: present a problem,
and if it is solvable, someone will solve it.
Is there any proof that life is not digital?
Behold! (Score:2, Funny)
Kids: So?
Mephisto: Those are HUMAN asses!
Kids: Ooooh!
The Secret of NIMH (Score:3, Funny)
Can't resist... (Score:5, Funny)
I am sure I am not the only one bothered by this.. (Score:5, Insightful)
This kind of research always frightens the snot out of me. Without trying to sound like a holier-than-thou type, I can't help but think that this type of science is dabbling a little beyond the realm of what we should be working on.
On the bright side, I would suspect that such organisms don't live long enough to make a whole lot of difference. Some odd hybrid creature created through such means would be bound to have some hideous problems.
Maybe there is some benefit to this type of research, where we will get better medicines, or a better understanding of how our own body is put together. That said, I disagree with the method.
Flame away.
It's the means (Score:2, Insightful)
The real question is whether our methods are sound or unsound -- not whether we should be there or not.
There are no realms of human knowledge where we should not be working. Who can make such a determination in the first place? The ways to get there, on the other hand, should be considered carefully but on a strictly secular level.
It's unfortunate that in the zeal to categorically ban all human cloning George Bush's administration has been unable to make this distinction.
The quest for knowledge must not be hindered by emotional, baseless "forbidden realms of knowledge" kind of arguments. If we allow that, the renessaince and enlightenment have been in vain and we're back in the dark ages burning witches.
Re:I am sure I am not the only one bothered by thi (Score:5, Interesting)
as a PhD-level biochemist/molecular biologist, i can tell you that seemingly pointless experiments such as these provide the necessary knowledge, or building blocks if you will, for us to understand the very complex process of growth and development. it's impossible to know to fix things if you don't know how they work and why they're broken.
you, the public, should know that any form of experimentation on any living thing with a backbone and a nervous system is *highly* regulated, as in many forms to fill out, a review committee, certification of the researcher following compulsory courses, etc.
it is unfortunate that the mainstream press *always* focus on the "freakish" aspect of science research, and not the "big picture". the bottom line is that in order for us to tackle the "big" issues in science and medicine, we need to experiment on living things. full stop, underline. of course i agree that there is an ethical aspect to certain areas of research that should not be neglected, but right now the ethical bar is being set way too low because of uninformed, negative spin on the part of the press.
we have been "genetically engineering" bacteria for over 20 years with no complaints nor public profile, and that research has directly and indirectly contributed immensely to various gene therapies and diagnostics, and to the mechanisms of viral and bacterial disease. the second that genetic engineering (improvement) of foodstuffs is mentioned, bang! alarm bells! when in fact, the bacterial and viral genetic engineering of the past 2 decades has posed a far greater risk of something going "wrong" or of some malevolent person engineering a super-ebola with a one week latency period (in which case we'd all be fucked big time). genetic engineering of food has the potential to solve or at least lessen the ongoing starvation of millions (while we continue to worry about whether we should upgrade to the latest video card...).
now take stem cell research. so what, stem cells. science operating the way it does, the vast majority of stem cells come from people who've died and/or aborted foetuses, not living creatures or "stem cell factories". i know, sounds icky, but stem cells are hugely important in terms of their scientific value and potential outcomes to mankind. and let's face it, once dead, a person's bone marrow is of no use to anyone else, right?
what society needs is some perspective. bush and gov can spin the ensuing iraq invasion in such a manner that many americans think it's kindof OK to *invade* a country and kill thousands of people for the sole reason that bush doesn't like their leader. if thousands of lives of living, breathing people can be wasted for oil, then why should we not make use of those passed away by natural causes to help the living? you.. your sister... your mother... your neighbour...
to be a scientist is to revere life and the process of living above all else. you should have more faith in us to do what is right. better yet, inform yourself about the issue or ask a friendly neighbourhood science pal and thrash out the real issues.
obviously, this is an issue close to my heart...
Re:I am sure I am not the only one bothered by thi (Score:5, Insightful)
You've just described popular opinion about most branches of science on the verge of breaktrhough, including biology (genetics) and particle physics (splitting the atom), among others. If we stopped science when it was deemed "beyong the realm of what we should be working on", we'd be living in caves.
Re:I am sure I am not the only one bothered by thi (Score:3, Interesting)
Absolutely. I worked in science for about ten years (in a field that genomic/protein research has all but taken over) and watched in horror as the investment dollars took over research.
Scientists today are not asking themselves why am I doing this but how much can I get for doing this? Then come the spin doctors (PR, marketing, bean counters, etc.) who hype the science as the greatest thing for humanity ever. Egads.
Doomsday? Probably. It appears we are playing with matches next to a giant bale of very dry hay.
As Samuel L. Jackson said in Jurrasic Park (hated the movie), 'hang on to your butts'.
Fritz Hollings? (Score:2, Funny)
No Registration (Score:2)
Why aren't the articles just posted like this to begin with? It's something that NYT themselves set up.
Re:No Registration (Score:2, Informative)
&partner=SLASHDOT [nytimes.com]
and so did you!!!
&partner=krnlpanic [nytimes.com]
Human Experimentation (Score:2)
babelfish (Score:4, Funny)
I shoved that into babelfish but it didn't come up with anything - no matter what language I selected...
Still unreleased ... (Score:2, Funny)
Just compile Human Interface Device support as a module.
VT:LTKV (Score:2)
Junior: "Not A Word."
Ethical Problems? They already do it. (Score:5, Interesting)
People complain and say that scientists should not make half-animal-half-man creatures and mix creatures. Just because it doesn't LOOK like some sort of chimera doesn't make it NOT a chimera.
Isn't antibody engineering and this the same thing?
Re:Ethical Problems? They already do it. (Score:3, Insightful)
Re:Ethical Problems? They already do it. (Score:3, Insightful)
That aside, we will have a problem as the line between human and animal blurs... Should we raise all animals to the level of humans wrt the rights they have? Probably not a good idea. I think we need to ignore the preachers, the churches, the "won't somebody think of the children" pretenders pushing for their own power, and set a strict definition of what defines a living, breathing, human being, and what is a clumb of cells related to, or with the potential to someday be a human being... I believe it's right for experiments to be done on month old foetuses, but I don't think it's right to do the same thing on one that could live if born prematurely....
perhaps I'm rambling and incoherent, I was just trying to raise a couple of points.
Re:Ethical Problems? They already do it. (Score:2)
What about doing medical experiments on your arm or groin? Neither could live if removed from your body. Neither your arm or groin are ever consulted and never have the chance to say anything about it.
Re:Ethical Problems? They already do it. (Score:3, Interesting)
So likewise, 'laws do not exist... They are a made up thing'?
Ethical problems do exist, but they are personal in nature. Societies choose which ethical concerns they collectively believe ought be enforced across the society. Generally such things are called laws.
we will have a problem as the line between human and animal blurs
There is no such line. Humans are and have always been animals. Its just that most humans believe that they are somehow 'more' than other animals (and most also believe that they are more than other humans too). The truth is that we are simply different.
Should we raise all animals to the level of humans wrt the rights they have?
That is precisely what many people assert. Such a move would obviously require that the entire population either go vegan or engineer and accept meat animals without even basic intelligence (I suspect this would be a great thing for food producers; all the meat and none of the behavour problems of 'real' animals).
Many people consider that beings that suffer (and that we can reasonably identify as suffering) ought not be caused, through our actions, to suffer.
From this point of view, early term abortion is pefectly ok, because the aborted material has not yet evolved to the point at which it is able to suffer.
I tend to agree with this viewpoint, to an extent. I don't think that the suffering of the mice outweighs the value of the research done with them. I'd prefer that they not be harmed, but at the moment it seems necessary. I would not take this position with animals with significantly more cognative power, such as apes.
Re:Silly me! (Score:2)
Re:Silly me! (Score:2)
Certainly not. The point of evolution is to ensure the propagation of the system. If the only route to that end is to reduce complexity, thats what will happen.
Another way to look at it is to consider that evolution is simply the mutations that happened to survive. Life is what happens to self replicating systems that don't terminate.
Everytime I ejaculate, I shed more human cells (Score:2)
I mean the whole idea of giving blood is to give cells. Either for another human to use, or to have those cells used for sume prupose--drug making--and then deliberately killed--i.e. sterilized defore being thrown away. Nothing immoral here.
It's human life that is precious, Not my little finger or some other unviable bit of flesh.
Re:Ethical Problems? They already do it. (Score:2, Insightful)
Second, I would submit that an even more striking example of the principle your presenting is the "Abgenix" mouse, a mouse whose IgG genes have been replaced by human genes so that the immunoglobulins it produces are clearly human. Also, type "human mouse hybrid" into Google and learn about murine cells with entire human chromosomes used to study telomerase
I guess the argument here is one of degree - many more human genes will be present in the hybrids described here. Also, they will be self-sustaining organisms in a way that cell lines really aren't. But on the whole I agree with you, this is just another step in a journey already begun.
Re:Ethical Problems? They already do it. (Score:2, Informative)
in truth, several similar things are done, but not approaching this scale, and not anything that would have the possibility (albeit remote) of creating offspring with cells that are entirely human.
Examples ...
(1) hybrids between murine (or other rodent species) and human cells. these experiments are typically done to map genetic factors unique to one organism or assay the recessive of dominant phenotypic nature of a gene factor. In long term culture, these are unstable. Mouse and human cells have different numbers of chromosomes which are duplicated at different speeds and move toward productive mitosis (somatic cell division) at different rates. The human chromosomes lag behind in the divisions and are eventually lost over time.
(2) immunologically crippled mice grafted with parts of the human immune system to study human immune function in an 'animal model'. These mice usually bearing the SCID or RAG genetic defect don't have an adaptive response/capability to recognize foreign cells as non-self. One popular model is the SCID-hu model in which mice typically are typically injected in their kidneys with human thymus, liver, and/or lymph node tissue in a capsule. There is partial immune reconstitution in these animals by the human immune system cells and they can be used in pathogen challenge or other studies. Obviously, potential progeny offspring would not genetically inherit human cells as a chimeric organism.
(3) Human genes can be introduced into mice as transgenes or by 'knock-ins' also more properly known as gene replacements. This is done to study human gene function in an animal context often looking at the cancer causing or cancer suppressing potential of genes of interest, the developmental role of particular genes, the immunological effect of genes, and more. These changes are very often heritable and there are many genetically altered mice currently available carrying numerous different human gene products
None of the examples above are on the scale of what is being considered in creating hybrid blastocysts between mouse and human. These are obviously most likely to be viable, but a concern I have is what happens when an enterprising individual takes it to the next level and successfully does the experiment using monkey (example was Rhesus) blastocysts ...what if human neurologic tissue is grafted
into this chimeric organism? This
type of research should not be taken out to an island run by a Dr. Moreau but
really needs to carefully considered before our science moves faster than our ability to comprehend
what we have created.
Obligatory Monty Python Reference (Score:2)
"Yes. The Mouse Problem [graphicszone.net]. This week 'The World Around Us' looks at the growing social phenomenon of Mice and Men. What makes a man want to be a mouse."
JPZ
HPD ? (Score:2, Offtopic)
Time to... (Score:3, Insightful)
Re:Time to... (Score:3, Insightful)
In any event, the key piece is constant experimentation, not just mental noodling. That stuff has to suffice for some kinds of physics & astronomy research, where the experiments can be difficult or impossible to do, but biology is so, well, wild & woolly, that the only way forward is to constantly test your ideas by experimentation.
Paging Mr. Steinbeck.... (Score:2)
Straight out of... (Score:2)
Unless using blastocysts from immunologically crippled mice, there would most likely be a recognition of non-self by murine immune cells not educated (which haven't seen during their development) to the human cells that would wipe them out.
"To make an alteration in the evolvment of an organic life system is fatal. A coding sequence cannot be revised once it's been established. by the second day of incubation, any cells that have undergone reversion mutations give rise to revertant colonies like rats leaving a sinking ship....Wouldn't obstruct replication, but it does give rise to an error in replication so that the newly formed DNA strand carries the mutation and you've got a virus again."
Really nice! (Score:2)
Research on human cells =! scary (Score:5, Interesting)
Methinks you've been spending too much time around George W. and his Department of Christian Morality. "A few cells" =! a human being. If human tissues are somehow sacred, I'd better make sure to never go for a biopsy lest my doctor and I be arrested for attempted murder!
Anyway, You can be assured that the researchers involved in this work, as well as their associated institutional ethicists, are acutely aware of the ethical issues involved here. I'm not saying we should let them decide if it's ethical, but it's not like they're cackling evilly in a secret laboratory, kidnapping blonde virgins to extract their stem cells and put them in giant killer mice. This is important basic research which could potentially lead to unanticipated advances in medicine and developmental biology. It would be foolish to condemn it because of some irrational "oh god no, human-mouse hybrids" reaction.
Re:Research on human cells =! scary (Score:2)
You're an idiot. (Score:2)
Trust me. Once someone throws open the door on this and makes the details of their research public knowledge, somebody, somewhere in this world of 6 billion people is going to attempt the unthinkable. Is it absolutely necessary that we open EVERY Pandora's Box, just because we can?
Don't worry, mice aren't animals. (Score:5, Interesting)
The actual exclusion is set down in 9 CFR part 1, and reads as follows:
"Animal means any live or dead dog, cat, nonhuman primate, guinea pig, hamster, rabbit, or any other warmblooded animal, which is being
used, or is intended for use for research, teaching, testing, experimentation, or exhibition purposes, or as a pet. This term excludes: Birds, rats of the genus Rattus and mice of the genus Mus bred for use in research, and horses not used for research purposes and other farm animals..."
Planet of the mice?? (Score:2)
hybrid? (Score:2)
Asimov already addressed this. (Score:4, Interesting)
-Peter
Re:Asimov already addressed this. (Score:3, Insightful)
Implications discussed some 60 years ago (Score:2, Interesting)
After these technique is as common as taking pills there is no sharply outline border between men and animals any more... Quite a different world...
You're all looking at this the wrong way. (Score:2)
Star Trek galore (Score:2)
(even if the terms relate to biotech instead of warp drives...)
I'm ready for it! (Score:2)
But, this already exists!!! (Score:2)
If they ain't votin' they ain't human - Wes Borg (Score:2)
TMNT (Score:2)
I want human-human hybreds (Score:2)
Burn a little Karma here (Score:3, Interesting)
I hope they do this. AND cloning, AND every other scientific experiment that might be interesting.
There is no such thing as bad knowledge, there is ONLY accurate or inaccurate DATA. ALL knowldege is good, ALL information should be propagated to every last human being on the planet. Holding back from knowledge, or any potential knowldege out of "fear" Religon" "National Security" or any other such quasi Pandorian bullshit is -to me anyway- being a traitor to the whole human race. I hope that every self proclaimed "ethicist" will someday be seen as merely another inquisitor slowing the progress of humanity out of the dark ages.
Am I the only one... (Score:2)
Re: (Score:2)
Serious question, please. (Score:2)
Frequently when matters of genetic manipulation make the news the media and other entities make objections based upon immorality. Ex: When cloning was more prevalent in the news, there were many people who were saying how wrong cloning a human would be, the huge implications it would have, etc.
However, after listening to their arguments I was left still wondering what exactly their objections were, apart from appeals to their moral beliefs. So: Could someone please give any actual reasons for opposing cloning?
Not a troll, it's just that usually whenever there is a moral objection to something there is at least a modicum of reason to back it up, even if it can be perceived as being somewhat specious. In the case of cloning I personally have seen none, specious or otherwise.
What is the Law? (Score:2)
Are we not men?
-Dr. Moreau
You know what this means don't you? (Score:4, Funny)
Fortunately I am almost finished designing a giant trap that will prey on the one weakness they neglected to genetically correct, Sweet, sweet, cheese.
This was achieved successfully long ago... (Score:2)
Foolish concerns (Score:2)
Isn't this being done on purpose to prevent it? (Score:2)
A. Make the goverment/people so sick that they would change the patent laws (and presumably other laws) to prevent such things.
B. Gain a patent and use it to prevent others from ever doing such a thing.
Here's a link:
http://www2.canisius.edu/~gallaghr/humouse.html
Coming soon.... (Score:3, Funny)
So how...? (Score:3, Funny)
For that matter, do they have balls or are they purely optical?
(There go my karma points...)
Re:A homozygous single copy murine immune mouse. (Score:2)
make super mice that can talk without using a throat
box computer diode space modulator.
Re:A homozygous single copy murine immune mouse. (Score:2)
Re:A homozygous single copy murine immune mouse. (Score:3, Informative)
It says:
Dipliod organisms (like all mammals including both humans and mice) have two sets of chromosomes and thus two copies of chromosome 1, two copies of chromosome 2, etc. Therefore if a particular mutation or altered gene is on, for example chromosome 3, then a mouse could have two copies of a normal chromosome (called a wild-type mouse), one normal and one altered chromosome (heterozygous), or two copies of the chromosome with the mutation (homozygous). Sometimes an animal homozygous for a certain mutation cannot survive to birth -- such a mutation is called "homozygous lethal." If the mutation is not homozygous lethal, and does not cause sterility, then one could raise a colony of mice that all have this particular mutation through selective breeding. The mice can then be examined to determine the phenotype -- or physical charactersitcs -- cause by the mutation.
and now the second sentence:
Whoever does this will have to use mice with no immune system othewise the mouse's immune system will recognise the embryonic stem cells that are introduced by the scientists as being forign and attack them. This is the same mechanism used by the body to fight off disease. (Translator's Comment: I dont think that is actualy true)