21 April 2003
Cloned Pigs Differ In Looks And Behavior
by Kate Melville
New research at North Carolina State University's College of Veterinary Medicine indicates that cloned pigs can have the same degree of variability in physical appearance and behavior as normally bred animals. Two separate studies show that while clones are genetically identical to the original animal, the similarities end there.
This dispels the commonly held notion that cloned animals retain the physical and behavioral attributes of the animal from which they were cloned. The research was conducted by Dr. Jorge Piedrahita, professor of molecular biomedical sciences at NC State, and colleagues at Texas A&M University. His study on cloned pig behavior, which appears in Applied Animal Behaviour Science, is the first published research on the behavior of cloned mammals. The study on cloned pig physiology, which appears in Biology of Reproduction, is the first study on clone physiology that included control subjects.
Piedrahita says the implications are far-reaching. "The technology of cloning has been sold to the public as a way of creating a group of identical animals and, as such, there are companies that have been set up around this concept, especially for pet cloning. The implication is that your cloned pet is going to behave and look like the one you already have - and that will not be the case," he said.
"We demonstrated in our behavioral paper that the behavior of clones is not identical. They are not homogeneous, so you cannot expect your cloned pet to behave like your original pet, even discounting environment. We've cloned animals that were raised in the same environment and they still didn't act the same," Piedrahita said.
In the behavioral study, two litters of cloned female pigs, consisting of five and four pigs respectively, and two control litters - each with four purebred pigs - were used. The purebred control pigs were of the same breed and sex and were born within the same week as their matched cloned litter. The cloned pigs were compared with the purebreds on a number of criteria such as food preferences and temperament.
In the physical study, the pigs were compared using a series of physiological and genetic parameters. The results indicated that while cloning creates animals within the normal phenotype - the appearance of an organism with respect to a group of characters - it increases the variability associated with some traits. "That means that you can't use cloned animals to reduce the size of groups involved in animal experiments," Piedrahita said.
Piedrahita says scientists must be very careful with cloning, since genetic errors can be introduced into the DNA of the clone during the process.
"Cloning advocates are calling them normal, healthy clones, but we don't think that is always the case. Some of those animals are going to be normal and very healthy but others will not. They are healthy enough to survive but that doesn't make them as healthy as non-cloned animals. At this point, we just don't have a lot of the answers," he said.
"While clones are genetically identical, physical characteristics such as size, weight and hair type may not be the same because the DNA has been modified during the cloning process in such a way that it affects the activity of certain genes," Piedrahita adds.
Piedrahita believes the behavioral and physiological variables will run throughout all cloned animals. "Any technology that's being sold that utilizes the clone itself, not the offspring of the clone, is the one that you have to be very careful with. That includes applications such as pet cloning, and the reproduction of high-production dairy cows or thoroughbred racehorses," he said.
Piedrahita says the benefits of cloning are better realized when the clone has offspring of its own. That's because any genetic errors are corrected, meaning that the original animal and the offspring of the clone will have the same genetic merit.
Piedrahita cites bull breeding as an example. "Say you have a dairy bull of high genetic merit so that, when mated with any cow, the offspring of that cow produces more milk. Now, let's say that bull produces very little sperm and has difficulty producing offspring. You could clone that animal, and then breed the clones. The offspring of the clones will have the same genetic merit as the original bull that allows cows to produce more milk.
"The bottom line is this: While clones are genetically identical, physical characteristics such as size, weight and hair type may not be the same because the DNA has been modified during the cloning process in such a way that it affects the activity of certain genes," he said.