Genetic engineering denotes the process of changing the genetic constitution of cells by introducing, modifying, or eliminating specific genes through modern molecular biology techniques. It is applied in several fields, including medicine and agriculture. Its application in medicine comprises the production of medical substances in genetically modified organisms, genetically modified animals as models for the study of human diseases, and gene therapy. In agriculture, it is used to improve food products in a variety of ways. Some of the well-known genetically modified foods are rice, soybeans, carrots, and tomatoes. Genetic engineering has not only become a major topic of biological anthropology, but has important implications on cultural and social anthropology as well; the most controversial issue is the direct nonmedical application of genetic engineering techniques to enhance normal function in humans.
Cells, DNA, and Genes
In the midst of the 19th century, modern biology was born on the basis of Charles Darwin’s theory of evolution and the finding that all living organisms are composed of cells. In the second half of that century, important discoveries were made in the fields of genetics and embryology, culminating at the turn of the century with the chromosome theory of heredity, which claims chromosomes are the structures that carry heredity information. From that point on, genetic research thrived. The chemical nature of the chromosomes, however, was unknown until 1944, when Oswald Avery and his colleagues used bacteria to demonstrate that genetic material is composed by deoxyribonucleic acid (DNA), which is found in all living organisms. In complex cells, DNA exists in the nucleus in the form of chromosomes (nuclear DNA) and in the mitochondria, structures found in the cytoplasm of cells (mitochondrial DNA). But without knowledge of the structure of DNA, little could be understood about how it actually worked.
This changed in 1953 with the discoveries by Jim Watson and Francis Crick. They could show that DNA is organized into two combined strands in the form of a helix, the now famous double helix. The strands are built by four bases only: adenine (A), guanine (G), cytosine (C), and thymine (T). These are linked together with sugar units and phosphates. Moreover, the two strands are complementary: The sequence of the bases of one strand determines unequivocally the sequence of the other, due to the chemical affinity of the bases. Base pairs can form only between A and T and between G and C. This is essential to DNA’s ability to duplicate and make an exact copy of itself (a process called replication). In this process, the two halves of the helix separate, and a new partner is fabricated to match each half exactly.
DNA controls unique features of an organism. Each cell of an organism contains the exact same DNA sequence, in which the instructions for certain gene products are encoded. There are systems in cells that read the DNA sequence and “translate” it into proteins (linked amino acids). Proteins then go on to be effective in many ways. Some are structural components of tissues (like collagen, a structural material of bone and many other tissues). Some are enzymes that initiate and enhance chemical reactions (like lactase for digestion). DNA contains the instructions, and proteins carry out the instructions. The process by which the DNA instructions are converted into the structures and functions of a cell is called gene expression. The rule by which the DNA sequence is translated into a protein is called the genetic code. This code is the same in all known living organisms. An organism’s life, growth, and unique features depend on its DNA. A segment of DNA coding for defined information is called a gene. All the genetic material of an individual or species is called its genome.
In many species, however, only a small fraction of the genome’s total sequence encodes protein. And with those that do, not all information is actually used for protein synthesis. Contained within DNA sequences are elements, known as promoters and repressors, which allow individual cells to control which genes are expressed. Expressing genes in the appropriate tissue at the appropriate time is very important. In the human body, for example, regulation ensures that fingernails grow only on fingers and hair grows only on specific parts of skin. But although genes determine many characteristics of an organism, we do not yet understand how specific genes contribute to the complex physical, cognitive, emotional, and behavioral traits of humans.
Types and Techniques of Genetic Modification
The alteration of DNA allows genetic engineers to change the genetic constitution of cells. Since DNA is passed on from one generation to the next, changes in DNA can be carried over generations. In this respect, however, an important distinction in genetic engineering occurs between germ line and non-germ-line cells. In most organisms, certain cells are set aside exclusively for reproduction. These are called germ line cells (in humans, the eggs and sperm). Nongerm-line cells are all the other cells in the body, muscle cells, skin cells, liver, and so on. If a genetic modification does not alter germ line cells, it has no effect on the genetic makeup of future generations. Genetic engineering is performed on germ line or non-germ-line cells, depending on the purpose of intervention.
Two basic types of genetic modification are the addition or deletion of function. To add a function to a cell, all that must be done is to introduce a new gene that codes for the given function. Deletion of function can be performed by either knocking out a gene or introducing an antisense gene to interfere with the cell’s ability to express a given gene. Although genetic engineering has a wide range of applications, only a few fundamental steps are required. These include the isolation of the donor DNA of interest and its amplification, transfer, and expression in a host cell.
The major tools for the isolation of the donor DNA are so-called restriction enzymes. They work by cutting up the DNA, a process called restriction. Most of them are very specific. They recognize short, specific sequences in DNA and cut at specific points within these sequences. For most tasks, the amount of DNA fragments that can be obtained from a cell is not enough; amplification is needed. Therefore, one of the most important practical developments in genetic engineering is the polymerase chain reaction (PCR), an achievement for which its inventor, Kary Mullis, was honored with the Nobel Prize in Chemistry. Using PCR, any short sequence of DNA can be amplified many times. Because even single DNA molecules can be amplified through PCR, the method is also applied in archaeology, forensic anthropology (the application of anthropological techniques to legal matters), and paleoanthropology (the study of earlier hominids). For example, anthropologists have been able to analyze mitochondrial DNA sequences of the Neandertals.
There are a number of techniques for introducing genes artificially into host organisms. Some use biological vectors (organisms to transport donor DNA), like plasmids or viruses. Plasmids are small circular pieces of genetic material found in bacteria that have the ability to cross species boundaries. Viruses are infectious particles, specialized over millions of years, that contain genetic material to which a new gene can be added. The vector DNA and the fragmented donor DNA are brought together. Afterward, the new combination of DNA in the vector is transferred into the cells of a host organism, in which the cells with the new genetic information are reproduced and the new genetic information is expressed. Such techniques have been around since the 1970s. Nonbiological methods of transfer comprise chemical and physical procedures. In electro- and chemicalporation, pores or holes in a cell membrane are created to allow entry of the new genes. The method is now widely used with microorganisms, plants, and animals. So-called projectile methods use metal, such as gold, slivers, which are coated with the genetic material to be transferred.
One projectile method, called biolistics, propels the coated slivers into the cell using a shot gun. This method has become the main method of choice for the genetic engineering of many plant species. Another method, used especially with animals, introduces DNA into a cell via microinjection: The genetic material containing the donor DNA is directly injected into the host cell by use of a fine-tipped glass needle. With some methods, the means by which genes are inserted in the host organism may be inexact and occur at random. Therefore, methods have been developed to insert genes at specific spots in the genome of even complex organisms. Recombinase-mediated cassette exchange (RMCE), for example, performs site-specific chromosomal integration in mammalian cells. The expression in the host organism becomes predictable, because a single copy of the DNA inserted into the genome is integrated at a known site. Several types of bacteria are favored as host cells, but higher organisms, such as fungi, yeasts, mammalian, or insect cells, and whole animals or plants, can also be transformed by foreign DNA.
Since DNA is universal among organisms, it can be transferred between unrelated organisms. Genetic engineering enables scientists to create plants, animals, and microorganisms by manipulating genes in a way that does not occur naturally. It even allows genes to be moved across species lines or to move artificially constructed genes. An organism into which foreign DNA has been introduced is called a transgenic organism. The transfer of genes across distinct species is called horizontal gene transfer. While in theory, the technology is available to transfer a particular gene from any organism into any other, in actual practice, there are numerous constraining factors. The single most limiting factor is the dearth of basic scientific knowledge of gene structure and function.
Applications of Genetic Engineering
Techniques of genetic engineering are applied in both the research and practice of medicine. In practice, for many years, genetic engineering has made it easier to gain various medical substances that are produced by bacteria, such as insulin, for example. As explained above, plasmids augmented with new genetic material can move across microbial cell boundaries and place the new genetic material next to the bacterium’s own genes. Often, the bacteria will take up the gene and begin to produce the protein for which the gene codes. If the new gene codes for insulin, the bacterium will begin to produce insulin. In addition, transgenic animals are used to produce medicine through the process known as gene pharming. Genetically altered sheep, for example, produce an enzyme in their milk that is present in most people and prevents a serious form of emphysema. Extracted from the milk and purified, it can be helpful to people who do not normally produce it. In general, genetic engineering provides the basis for a well-founded biological-causal understanding of certain diseases, thus opening up the development of new effective treatments oriented on the cellular-molecular causes of a disease. These are the hopes of gene therapy. Gene therapy is a technique for correcting defective genes responsible for disease development. Such therapies often try to replace or repair defective genes. In most gene therapy studies, a “normal” gene is inserted into the genome to replace an “abnormal,” disease-causing gene. Hopes are high for some diseases (Parkinson’s or Huntington’s, for example), but gene therapy is still experimental. When gene therapy does not alter the germ line but only somatic cells (somatic gene therapy), the disease can still be inherited by children. In contrast, this is no longer possible when gene therapy is applied on the germ line level (germ cell gene therapy). At the moment, germ cell gene therapy is banned in many countries. The same holds for xeno-transplantation, the transplantation of tissues and organs between species (for example, the use of a swine heart for a human). Here, genetic engineering plays a crucial role, because in order for this technique to work, it is necessary to knock out most of the strong, ordinary antigenic systems in swine. In medical research, transgenic animals have become important models for the study of human diseases, like cancer, multiple sclerosis, and diabetes. Due to its physiological closeness to man and its simple breeding, the mouse is the most common transgenic animal. However, there are also transgenic strains of farm animals, such as chickens, pigs, sheep, goats, and cattle.
Genetic engineering techniques have also been used to improve food products in a variety of ways. Some of the well-known genetically modified foods include rice, soybeans, carrots, and tomatoes. In agriculture, useful plants are optimized by genetic engineering through the addition of a resistance against pesticides or resistance against pests. Sometimes genes are transferred to add other useful characteristics in growing. Tomatoes are an example. These are sensitive to frost, and this shortens their growing season. Fish, on the other hand, can survive in very cold water. Scientists identified a particular gene that enables a flounder to resist cold and used the technology of genetic engineering to insert this “antifreeze” gene into a tomato. This makes it possible to extend the growing season of the tomato. Sometimes, genes are added to provide extra nutrients, like in “golden rice,” a genetically modified rice that contains building blocks for vitamin A. Deficiency in this vitamin causes blindness and other diseases. Moreover, sometimes a gene is removed to enhance a product, such as removing the tear-producing element of onions.
Cattle and pigs are commonly treated with genetically engineered growth hormones to increase growth rates. A lot of other industries use genetically engineered products as well. For example, genetically engineered enzymes are used in the production of cheese and bread, in laundry soap, in the bleaching of jeans, and in the treatment of leather.
Genetic Engineering and Anthropology
What is already possible and what is probable to be possible in the future are both related to anthropology in various fields and ways. Biological anthropology includes the exploration of the implications of modern advances in genetics, including genetic engineering. For anthropological research, genetic engineering is a method to explore basic biological mechanisms, such as yet unknown principles of genetics. Biological anthropology also places particular emphasis on the interaction between biology and culture; for biological anthropologists, genetic engineering will help in understanding the complex relationship between biological constitution, culture, and environment. On a more future-oriented and general level, it is questioned whether genetic engineering poses evolutionary dangers and how it will change the understanding of evolution itself, what it is, and how it operates. Will traditional evolution be replaced by “intelligent design”? Will genetic engineering change the relationship between humans and other species? However, biological anthropology is not the only field concerned with genetic engineering. Social and cultural anthropology are interested in the social and cultural implications of genetic engineering. Genetic engineering is controversial due to numerous questions related to product safety, and environmental and social concerns. Many aspects are still poorly understood and unexpected side effects may occur. More controversial still is the direct application of genetic engineering techniques on humans and especially the possible nonmedical applications for the enhancement of normal functions. Some see genetic engineering as a new tool for eugenics, the doctrine or practice of selective breeding in order to “improve” the human genetic pool. The effect genetic engineering will have on societies is a huge field of anthropological study.
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