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.
The research was supported by a grant from the National Institutes of Health.
Note to editors: Abstracts of the behavior paper and the physiology paper follow.
"Behavioral variation among cloned pigs"
Authors: Gregory S. Archer and T.H. Friend, Texas A&M University; J. Piedrahita, North Carolina State University; C.H. Nevill, S. Walker, Texas A&M University
Published: Feb. 19, 2003, in the early online edition of Applied Animal Behaviour Science
Abstract: The variability of behavior among cloned animals has yet to be studied. Through a series of behavior tests, we quantified the variation in food preference, temperament, and time budgets of two genetically identical Duroc litters (n=5, 4) and their naturally bred controls (n=4, 4). All litters of pigs were tested for their food preference using apples, bananas, crackers, and carrots. Variation in temperament was determined by timing latency to remove a towel (Towel Test) and by counting vocalizations and escape attempts during Back and Pick-up Tests. Seventy-two hours of time lapse video were used to determine time budgets of the pigs consisting of the following behaviors: lying in bedding, lying on concrete, standing, feeding, and play/fighting. An F-test was used to determine differences in variation between litter variations. The clones were similarly or more variable (P<0.05) than the naturally bred controls: in their preference for the foods in 13 of the 160 comparisons; in 5 of the 8 comparisons during the Towel Test; in all four comparisons in the Back and Pick-up Tests; and in 9 of the 10 comparisons in the time budget analysis. These results reinforce the importance of environmental effects on animal behavior and question the use of cloning by nuclear transfer to replicate animals with specific behavioral characteristics.
"Hierarchical Phenotype and Epigenetic Variation in Cloned Swine"
Authors: Greg S. Archer, Scott Dindor, Ted H. Friend, Shawn Walker, Gretchen Zaunbrecher, Bruce Lawhorn, Texas A&M University; Jorge A. Piedrahita, North Carolina State University
Published: Accepted by Biology of Reproduction
Abstract: It has been determined that cloning by somatic cell nuclear transfer can result in the birth of animals with phenotypic and gene expression abnormalities. We have compared adult clones and adult pigs from naturally bred control females in using a series of physiological and genetic parameters including detailed methylation profiles of selected genomic regions. Phenotypic and genetic analyses indicated that there are two classes of traits, one where the clones have less variation than controls, and another characterized by variation that is equally high in cloned and control pigs.
Our results indicate that while cloning creates animals within the normal phenotypic range, it increases the variability associated with some traits. This is contrary to the expectation that one potential use of cloning is to reduce the size of groups involved in animal experimentation, as well as the use of cloning to reproduce an animal, including pets, with a homogenous set of desired traits.
Media Contacts:
Dr. Jorge A. Piedrahita, 919-515-7407
Greg Thomas, News Services, 919-515-3470
Journal
Biology of Reproduction