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Cloning

I just lost my cat. So, I intend to clone him, one day. So for now I've kept it in the freezer. Thing is, the shock, deciding whether I should bury him or clone him etc took me one and a half hours. So my question is, is there major degradation of the DNA within that time?

-A high school student from Texas

October 11, 2005

In some ways, your instinct was right on. If your cat's DNA gets too beat up, you wouldn't be able to clone your cat. So, you lower the temperature to slow down the process of DNA degradation.

Unfortunately, DNA isn't enough for cloning (at least not yet). The six feet of DNA jammed into the tiny nucleus of a cell has to be folded just right to work and scientists don't know how to fold it. Only the cell can do that.

So for right now, we need a live cell with an intact nucleus. And improper freezing destroys the nucleus and makes it nearly impossible to bring a cell back to life. (In a refrigerator, a cat can still be cloned up to 5 days after passing on.)

To understand why DNA alone isn't enough, it is important to know how cloning works. Let's look at the specific process used by the now out of business cat cloning company, Genetics Savings & Clone (GS&C).

First off, a veterinarian gets some cells from the animal that is going to be cloned. The vet sends the cells to GS&C and they then grow these cells up in a dish and freeze them off for the day when the cloning will happen. The scientists freeze the cells but do it in a way so that ice won't destroy the cells and their precious nuclei.

Once they are given the go ahead, the scientists next thaw out some of these cells. To use the cells for cloning, the cells need to be treated so that certain markings on the DNA disappear.

These markings are what make a skin cell a skin cell, a heart cell, a heart cell, etc. (click here to learn more about these marking). Scientists can, for example, make a skin cell forget it was a skin cell by wiping out these markings.

The DNA in this cell can now be programmed to be any kind of cell -- it is a clean slate like the DNA in an embryo. This "virgin" DNA is now ready to become a cloned cat.

Except this cell can't be grown into a cat -- its DNA needs to be transferred to an egg. The egg has all sorts of goodies needed to start the process of growing an animal. 

The next step is to take out an egg's nucleus and put in the treated cell's nucleus. Actually, GS&C fuses the egg cell and the treated cell but you get the same result -- an egg with a new nucleus.

This egg is now put into a surrogate cat where it will grow. The new cat that is born at the end of the pregnancy is a clone of the original cat -- it has the exact same DNA.

From this you can see why it is so important to have intact cells. There isn't any way to perform this procedure with a broken or dead cell.

Now I might have done the same thing as you in the heat of the moment. Especially when you hear about scientists thinking about cloning a wooly mammoth. What is most frustrating is that the reason they think they can clone the mammoth is because it is frozen!

So why a wooly mammoth but not your cat? As I read about cloning a mammoth I realized how much hype is involved. For the most part, people are talking about cloning it from DNA, something that has never been done before.

As I've said, no one has ever taken just the DNA of an animal and used it to clone that animal. All cloning done to date has been done with an intact nucleus. Of course if they figure out how to clone a wooly mammoth from its DNA, then there may be hope for your cat in the future.

The other way that people talk about "cloning" a wooly mammoth isn't really cloning it at all. It is more about making an elephant/mammoth hybrid.

The idea is to fertilize an elephant egg with frozen (well, thawed) wooly mammoth sperm. Then they would keep cross breeding until they got something that is mostly mammoth. Sperm is pretty hardy but this seems farfetched as well. I'm not sure if anyone has even tried to get sperm from a recently frozen animal let alone a 4000 year old one.

No, the best hope for your cat and the wooly mammoth is that science will advance to the point where we can use DNA and not live cells or nuclei. Seems like it will be far in the future but that's what I thought about Dolly the sheep too...

By Dr. Barry Starr, Stanford University

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