Genetic engineering is being implemented to create animals that have had a new gene inserted directly into their DNA. These animals are called transgenic. The procedure involves microinjection of the desired gene into the nucleus of fertilized eggs. It has been found that in many cases, but with varying rates of success, the new gene is reproduced in all developing cells, and the gene can be transcribed (which means the information contained in the gene can be read and utilized by the cell). This is a startling breakthrough in animal breeding endeavors, because it means a specific trait can be incorporated into a population in a single generation, rather than the several generations this takes when conventional breeding techniques are used.
However, there are some serious limitations to the procedure. The first of these has to do with the manner in which many genes work together to produce most traits. In fact, there are very few traits a breeder would like to include in an animal population that involve only one or two genes. Although it might some day be possible to incorporate any number of genes into an embryo's DNA, the complex interplay of genes is not understood very well, and the process of identifying all of the genes related to a desired trait is costly and time-consuming.
Another problem in the production of transgenic animals is that they pass their modified DNA on to their offspring with varying success rates and unpredictable results. In some cases, the new gene is present in the offspring but it is not utilized. The new gene may also be altered or rearranged in some way, probably during the process of gamete production.
These factors have made it difficult to successfully produce a transgenic strain of animals. However, with further research into the mechanism by which the gene is incorporated into the genome, and by successfully mapping the target animal genome and identifying the genes responsible for various traits, genetic engineering will no doubt become a major tool for improving animal strains.
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