© 1998, 1999 Gregory Carey Chapter 7: The New Genetics - 1 Chapter 7: The New Genetics—Techniques for DNA Analysis Introduction Before the 1980s, finding the genotype of an individual usually involved various laboratory assays for a gene product—the protein or enzyme. The cases of the ABO and Rhesus blood groups are classic examples of how one infers genotypes from the reaction of gene products with certain chemicals. In the mid 1980s, genetic technology took a great leap forward with the ability to genotype the DNA itself. The geneticist could now examine the DNA directly without going through the laborious process of developing assays to detect individual differences in proteins and enzymes. Direct DNA analysis had the further advantage of being able to identify alleles in sections of DNA that did not code for polypeptide chains. As a result of these new advances, the number of genetic loci that could be detected increased exponentially and soon led to the identification of the genes for disorders that had remained a mystery for the better part of this century. In this chapter, the major molecular techniques are outlined. The purpose is to provide a quick and understandable reference for the social scientist. The content of this chapter is not something that is required to understand genetics, what genes are, or how they relate to human behavior. Indeed, this chapter may be skipped without any great loss of continuity. Hence, only the essentials are given and the reader interested in the laboratory science behind the techniques is referred to contemporary textbooks on molecular genetics. We begin by defining a series of basic tools and techniques. © 1998, 1999 Gregory Carey Chapter 7: The New Genetics - 2 Basic Tools and Techniques: Basic tools: Electrophoresis Electrophoresis is a technique that separates small biological molecules by their molecular weight. It may be applied to molecules as large as proteins and enzymes as well as to small snippets of DNA and RNA. One begins the procedure by constructing a “gel”—a highly viscous material the actual chemistry of which need not concern us. Purified copies of the biological specimen are then injected into a “starting lane” at one end of the gel. Finally, a weak electric current is passed through the gel for a specified amount of time. Gravity and the electric current cause the biological molecules to migrate to the opposite end of the gel. The extent to which any molecule moves depends upon its electrical charge, molecular weight, the viscosity of the gel, the strength of the current, and the amA. The simplest method to denature DNA is to h33///////////////////////(http://psych.colorado.edu/~carey/hgss/hgsschapters/HGSS_Chapter07.pdf) # cited
RNA and DNA-RNA hybrids are more dense than simply DNA if the density of different nucleic acids is tested using a CsCl gradient.
The primary technique employed in molecular biology is the extraction of DNA, RNA, and protein. Scientists can separate materials according to size, shape, and density by using density gradient centrifugation. Isopycnic centrifugation, a sort of density gradient centrifugation that Meselson and Stahl developed, employed a cesium chloride solution to separate DNA molecules solely on the basis of density. Because DNA has hydrogen bonds between its strands, which makes it less dense than RNA, RNA has a far larger density than DNA. RNA can be obtained at the test tube's bottom using a CsCl density gradient and high centrifugation, whereas DNA can be recovered in the middle layer.
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