Aside from splitting embryos to produce more offspring, the main application of cloning to date has been to obtain basic biological information that can be applied in other areas. This will continue to be the main value of cloning for some time, and will result in information about causes of birth defects, aging, cancer, and other disease states.
One obvious application of cloning by nuclear transplantation and cell fusion is to make genetic copies of outstanding agricultural animals. As discussed earlier, a genetic copy does not equal a phenotypic copy, so this is not nearly as attractive as most people surmise. For example, the genetic contribution (heritability) to differences between cattle (within breeds) in milk production is on the order of 30 percent, while other factors, mainly environment and random chance, explain the other 70 percent. Thus, if one cloned a cow producing 3,000 gallons of milk annually, selected from a herd averaging 2,000 gallons of milk, on the average only 30 percent of the difference between the production of the individual cow and the herd would show up in the clone. A herd of such clones might average 2,300 gallons of milk, a substantial improvement over the 2,000 gallons average, but not even close to the 3,000 gallons produced by the animal being cloned. (This example is an oversimplification, for a variety of reasons—including interactions between genotype and environment [see Lewontin]— but the broad idea is correct.)
There is an even more serious problem with using cloning to increase production of milk (or meat, fiber, etc.), which is that it is not economically viable. The value of the extra milk produced by such a cow would be less than $1,000 during her lifetime, and she might eat more feed than other cows because more nutrients are required to make more milk, further decreasing her economic value. Costs of cloning in 2003 are in excess of $10,000 per cow, and while this likely will decrease markedly, it is unlikely that costs will approach economic viability in the foreseeable future. Thus, herds of cloned cows are not likely any time soon. The situation for meat production is even less favorable economically. If one did use this strategy, there would be hundreds of different donor cows cloned due to wanting different optimal genotypes for different environments (e.g. the optimal Vermont cow would be different from the optimal cow for Georgia) not to mention the individual preferences of farmers).
One agricultural application that does make sense is to make copies of genetically (as opposed to phenotypically) outstanding individuals. A good example is a bull whose daughters, on the average, have excellent milk production and are not prone to mammary gland infections. Such a bull might have thousands of daughters demonstrated to be superior to the average population. This bull obviously is essentially worthless phenotypically—copies will not produce any milk—but cloned copies of the bull will produce essentially identical sperm that can be used to produce more daughters by artificial insemination. For this example, one or two clones would likely produce all the semen that could be sold, so large numbers of copies are not needed. In fact, the main application in this context is insurance. Such bulls are extremely valuable, and having one or two copies makes good economic sense. More copies, however, are redundant and expensive to feed and maintain.
Another popular potential application of somatic-cell cloning concerns companion animals, particularly dogs and horses. Again, one will not get a phenotypic copy, so this only makes marginal sense. The resulting cloned animal will often have somewhat similar coat-color patterns and be roughly the same size, but it may have a very different personality, since this is largely influenced by environment. One does not recreate the same animal by cloning, simply a chromosomal genetic copy.
There are myriad experimental uses of cloning, particularly in making transgenic technology more useful. Cloning by nuclear transplantation is thus a powerful experimental tool.
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