THERE is much talk about new discoveries in the field of genetics. Since the development of powerful microscopes that enable men to probe deeper into the world of the unit of life, the cell, and to see features that they never before knew existed, some researchers and journalists have theorized that men may be able to discover the complete genetic code, even the “secret of life.” They extend their speculations, even forecasting that, by genetic manipulation, they will be able to cure hereditary diseases and defects and, possibly, make a race having superior bodies and intellects.
Some things have been done with the very simple life forms by way of genetic interference. But scientists almost unanimously admit that they are far, far from manipulating the genes of the human cell so that they can correct deficiencies. Let us examine a few of the things that have been done.
The word “clone” means a group of organisms produced without sexual union from a single ancestor. In nature clones are found in organisms capable of asexual reproduction, that is, in certain plants and bacteria. The offspring inherit their genes from one parent. Therefore all individuals in a clone are genetically alike. Artificial cloning has been done with animals that reproduce sexually, such as sea urchins, salamanders and frogs. An egg cell is enucleated, that is, the nucleus is removed and replaced with the nucleus from the body cell of an animal of the same kind. But in every case, the nucleus taken from the body cell of an animal, and inserted into the egg of another, has to be taken at a very early stage in all but extremely simple life forms. This is because, slightly later, yet still at an early stage in the development of an embryo, the cells become differentiated or specialized and will not serve for cloning of a total new individual. Why? For the reason that, although every body cell has the full complement of chromosomes, the differentiated cell cannot function in other parts of the body. This is because the genetic code on its chromosomes will work for only that part of the body that the cell is specialized to serve. When placed in the enucleated egg, the cloning attempt will fail. Monroe W. Strickberger of Saint Louis University, in his book Genetics, says about cloning:
“The cells of early sea urchin embryos, for example, can be isolated from each other at the two- and four-cell stages and nevertheless develop into complete embryos. In salamanders, Spemann showed that a single cell at the embryonic 16-cell stage could produce an entire embryo. More recent experiments by Briggs and King have shown that some nuclei from blastula and gastrula [very early] stages of frog embryos (Rana pipiens) are still sufficiently potent to produce a complete embryo when transplanted into an enucleated egg. In Xenopus laevis, the African clawed frog, Gurdon has shown that at least 20 percent of the intestinal cells of feeding tadpoles can be transplanted and produce functional muscle and nerve cells. Furthermore, some of these intestinal cells may even produce a completely viable embryo. In plants Steward has found that individual carrot root cells can, with proper nourishment, be made to differentiate into complete carrot plants. In Drosophila [a vinegar fly] Hadorn has shown that larval embryonic discs which would ordinarily develop into genital tissue, for example, will, after many successive transplantations, develop into other tissues as well, including parts of the head, thorax, legs and wings.”
Note, in Strickberger’s comments, that, in order to achieve successful cloning, the nuclei must be taken from a sea urchin when it is only in the two- to four-cell stage, and from a salamander embryo when it consists of only 16 cells—yet very tiny. The nucleus must be taken from the blastula and gastrula stages of frog embryos (at this point no semblance or form of the creature is distinguishable). Cells of these stages soon after conception must be used because, after a cell becomes differentiated and starts doing its specialized work in a certain part of the body, it will not serve as do the younger cells, not being versatile enough to produce all parts of the individual, in this case a frog. In one species of frog, the Xenopus laevis, a very small percentage of intestinal tadpole cells may produce a complete embryo that will live. (A tadpole is an early, immature form of a frog.) In the case of Drosophila, the vinegar fly or “fruit fly,” genital tissue from larval (early wormlike stage) embryonic discs, only by successive transplantations, will develop into other tissues with which it is associated by transplant, but not into complete embryos.
As to cloning in humans, biologists do not claim that this can be done, or that they are anywhere near doing so. Some uninformed persons, apparently for sensationalism, have envisioned cloned populations of humans, directed by genetic engineers, in which only the most desirable personality traits exist. Some have theorized that persons like Einstein—mental prodigies—or great athletes—could be duplicated by cloning. But note that, even in the lowly sea urchin or the salamander, the cells have to be taken at the blastula or the gastrula stage—very early embryonic stages, for successful cloning. Who would know at the blastula or gastrula stage of a child’s formation whether he would turn out to have “Einstein-type” intelligence? At that early period of growth, there is not even a semblance of human form, and it is impossible to know then whether the individual will be healthy and intelligent, or deformed, imbecilic and of the poorest quality.