|
The responses to the questions provided in this document represent the FDA’s view in light of the conclusions and recommendations outlined in the Draft Animal Cloning Risk Assessment, Proposed Risk Management Plan, and Draft Guidance for Industry #179. Based on the comments received in response to these draft documents, FDA may revise its conclusions and recommendations. If such changes are needed, the responses to some of the following questions may also need to be revised. |
Cloning is a new technology.
Actually, cloning isn’t new at all. In fact, we eat clones all the time, in the form of bananas and grafted fruits. We’ve been cloning plants for decades, except that we refer to it as “vegetative propagation.” It takes about 30 years to breed a banana from seed, so, to speed the process of getting fruit to market, most bananas, potatoes, apples, grapes, pears, and peaches are clones.
Some animals can reproduce themselves by vegetative propagation, including starfish and other relatively simple sea creatures. Amphibians such as frogs first underwent cloning in the 1950s. Identical twin mammals can be thought of as naturally occurring clones, but producing clones of mammals in the laboratory is relatively new. Using cells from animal embryos to make clones has been has been around since the early 1990s, but the first animal cloned from an adult was Dolly the sheep, who was born in 1996.
Clones are a specific animal’s DNA grafted onto another body.
Absolutely not. Despite science fiction books and movies, clones are born just like any other animal. The only difference is that clones don’t require a sperm and egg to come together to make an embryo. Clone embryos are made by using a cell from a donor animal and fusing it to an egg cell that’s had its nucleus removed. That embryo is implanted into the uterus of a surrogate dam (female animal that gives birth) to grow just as if it came from embryo transfer or in vitro fertilization.
Offspring of clones are clones, and each generation gets weaker and weaker and has more and more problems.
No, not at all. A clone produces offspring by sex just like any other animal. Whether or not one or both parents are clones has no impact on the offspring.
Breeding clones by sexual reproduction is not like copying a paper document. One way to think about this is to imagine identical twin female cows (which are naturally occurring clones). When these two cows get bred, the offspring of one twin aren’t weaker or more damaged than the other. They have some characteristics from their sire, and some from their dams. They aren’t “part twin,” (or “part clone”); they’re just cows.
Clones are always identical in looks.
Not necessarily. In fact, many clones have slight variations in coat color and markings.
Let’s think about the identical twin calves again. They have the same genes, but look a little different. That’s because of the way those genes are “expressed.” For example, if they’re Holstein cows, the pattern of their spots, or the shape of their ears may be different. Human identical twins also have the same genes, but because those genes are expressed differently in each person, they have different freckle and fingerprint patterns.
Clones have exactly the same temperament and personality as the animals from which they were cloned.
Temperament is only partly determined by genetics; a lot has to do with the way an animal has been raised. It’s the old “nature versus nurture” argument.
Say you want to clone your horse because of his gentle and sweet temperament. Although your horse’s clone may be laid-back and easy-going, he would have to have exactly the same life experiences as your original horse in order to have the same temperament.
Your original horse isn’t afraid of loud noises because his experiences have taught him that they won’t hurt him. But if your clone has a bad experience with loud noises (say that a tree branch falls on him in a loud thunderstorm and hurts him), he may associate loud noises with pain and be afraid of them.
When clones are born, they’re the same age as their donors, and don’t live long.
Clones are born the same way as other newborn animals: as babies. No one really knows what causes aging in mammals, but most scientists think it has to do with a part of the chromosome called a “telomere” that functions as a kind of “clock” in the cell. Telomeres tend to be long at birth, and shorten as the animal ages.
A study on Dolly (the famous sheep clone) showed that her telomeres were the shorter length of her (older) donor, even though Dolly was much younger. Studies of other clones have shown that telomeres in clones are shorter in some tissues in the body, and are “age appropriate” in other tissues. Still other studies of clones show that telomeres are age appropriate in all of the tissues. Despite the length of telomeres reported in different studies, most clones appear to be aging normally.
Cloning results in severely damaged animals that suffer, and continue to have health problems all their lives.
In the early days of what is known as assisted reproductive technologies in livestock, veterinarians noticed that some calf and lamb fetuses grew too large during pregnancy, and had serious birth defects. This set of abnormalities is referred to as “Large Offspring Syndrome”. These same abnormalities have also been seen in cloning, and have received a lot of attention, because they occur at what appear to be higher rates than observed with other assisted reproduction such as in vitro fertilization. The syndrome seems to be related to processes that take place “in vitro” or outside the body. As producers understand more about the cloning process, the rate at which LOS is observed in clones has been decreasing. The same kind of decrease in LOS rates was observed as people who used technologies such as in vitro fertilization in cattle learned more about the process. LOS hasn’t been seen in pig or goat clones.
If clones survive the first few days after birth, they become as strong and healthy as any other young animals. When they’re young adults, they’re completely indistinguishable by appearance and blood measurements from conventional animals of the same age.
Cow clones make human pharmaceuticals in their milk.
Lots of people get this confused. The clones we’re talking about here are “just clones.” They don’t have any new genes added to them. Cows that make pharmaceuticals in their milk are genetically engineered—that is, they have new genes added to them. Some of these genetically engineered animals can be reproduced by cloning, which is why some people get confused about this. Animals that are “just cloned” don’t make pharmaceuticals (or any other non-milk substances) in their milk. They just do the same thing as their conventional counterparts.
When a chicken clone lays eggs, the chicks that hatch are clones.
Neither chickens nor any other kind of bird have been cloned yet. So far, mice, rats, rabbits, cattle (and the closely related but endangered gaurs and bentangs), swine, sheep, goats, deer, horses, mules, cats, and dogs are the mammals that have been cloned.
Meat from clones is already in the food supply.
FDA has asked clone producers and breeders to voluntarily keep milk and meat from clones out of the food and feed supplies until we finish assessing their safety. To the best of our knowledge, they have been voluntarily keeping the milk and meat from clones out of the food and feed supplies. Further, clones are for breeding stock, so it’s not in a breeder’s best interest to put young stock into the food supply for sale as meat.
Cloning can cure diseases in livestock.
Cloning can’t directly cure diseases in livestock, but the cloning process may be one way to make a healthy copy of a valuable animal that has contracted a disease, been injured, or died. In addition, cloning may also be a way to duplicate a disease-resistant animal, and over generations create a disease-resistant herd.
Scientists can bring back the extinct species by cloning them.
Although it’s theoretically possible, at this time it’s not very likely to happen. There are multiple technical barriers to doing this. First, because of the relatively low success rate of cloning, you’d need hundreds to thousands of cells from the extinct animal. Further, those cells would have to have DNA that hadn’t degraded since the animals were last alive. Then you’d have to find a very, very closely related species to provide the egg cell whose nucleus would be removed. After that, you’d have to implant any dividing embryos into the “normal” development environment (You might be able to use an elephant to act as a surrogate dam for a wooly mammoth, but there is no modern animal comparable to a dinosaur.) Then, you’d have to hope that the surrogate dam didn’t reject the embryo as “too foreign.” So although it’s possible, we wouldn’t expect that you’d see this at this time or in the near future.
Well, okay, but how about cloning endangered species?
That’s not only possible, but it’s been done in some limited cases. Scientists have cloned sheep from very small populations, members of rare cattle breeds, and two species closely related to domesticated cattle species, the gaur and banteng.
|
||||||
 |
||||||
|
||||||