Sinopsis
Hardly a week goes by without a major news story involving a genetic breakthrough. The increasing pace of genetic discoveries has become staggering. The Human Genome Project is a case in point. This project began in the United States in 1990, when the National Institutes of Health and the Department of Energy joined forces with international partners to decipher the massive amount of information contained in our genome the deoxyribonucleic acid (DNA) found within all of our chromosomes (Figure 1.1 ). Working collectively, a large group of scientists from around the world produced a detailed series of maps that help geneticists navigate through human DNA. Remarkably, in only a decade, they determined the DNA sequence covering over 90% of the human genome. The first draft of this sequence, published in 2001, was nearly 3 billion nucleotide base pairs in length. The completed sequence, published in 2003, has an accuracy greater than 99.99%; fewer than one mistake was made in every 10,000 base pairs (bp)! Studying the human genome allows us to explore fundamental details about ourselves at the molecular level. The results of the Human Genome Project are expected to shed considerable light on basic questions, such as how many genes we have, how genes direct the activities of living cells, how species evolve, how single cells develop into complex tissues, and how defective genes cause disease. Furthermore, such understanding may lend itself to improvements in modern medicine by providing better diagnoses of diseases and the development of new treatments for them.
As scientists have attempted to unravel the mysteries within our genes, this journey has involved the invention of many new technologies. This textbook emphasizes a large number of these modern approaches. For example, new technologies have made it possible to produce medicines that would otherwise be difficult or impossible to make. An example is human recombinant insulin, sold under the brand name Humulin, which is synthesized in strains of Escherichia coli bacteria that have been genetically altered by the addition of genes that encode the functional regions of human insulin. The bacteria are grown in a laboratory and make large amounts of human insulin, which is purified and administered to millions of people with insulin-dependent diabetes. Chapter 20 describes the production of insulin in greater detail and also examines other ways that genetic approaches have applications in the area of biotechnology.
New genetic technologies are often met with skepticism and sometimes even with disdain. An example is DNA fingerprinting, a molecular method for identifying an individual based on a DNA sample (see Chapter 25 ). Though this technology is now relatively common in the area of forensic science, it was not always universally accepted. High-profile crime cases in the news cause us to realize that not everyone accepts the accuracy of DNA fingerprinting, in spite of its extraordinary ability to uniquely identify individuals.
A second controversial example is mammalian cloning. In 1997, Ian Wilmut and his colleagues produced clones of sheep, using mammary cells from an adult animal (Figure 1.2 ). More recently, such cloning has been achieved in several mammalian species, including cows, mice, goats, pigs, and cats. In 2002, the first pet was cloned, a cat named Carbon copy, or Copycat (see photo at the beginning of the chapter). The cloning of mammals provides the potential for many practical applications. Cloning of livestock would enable farmers to use cells from their best individuals to create genetically homogeneous herds. This could be advantageous in terms of agricultural yield, although such a genetically homogeneous herd may be more susceptible to certain diseases. However, people have become greatly concerned with the possibility of human cloning. As discussed in Chapter 20 , this prospect has raised serious ethical questions. Within the past few years, legislative bills have been introduced that involve bans on human cloning.
Finally, genetic technologies provide the means of modifying the traits of animals and plants in ways that would have been unimaginable just a few decades ago. Figure 1.3a illustrates a bizarre example in which scientists introduced a gene from jellyfish into mice. Certain species of jellyfish emit a “green glow” produced by a gene that encodes a bioluminescent protein called green fluorescent protein (GFP). When exposed to blue or ultraviolet (UV) light, the protein emits a striking green-colored light. Scientists were able to clone the GFP gene from a sample of jellyfish cells and then introduce this gene into laboratory mice. The green fluorescent protein is made throughout the cells of their bodies. As a result, their skin, eyes, and organs give off an eerie green glow when exposed to UV light. Only their fur does not glow.
The expression of green fluorescent protein allows researchers to identify particular proteins in cells or specific body parts. For example, Andrea Crisanti and colleagues have altered mosquitoes to express GFP only in the gonads of males (Figure 1.3b). This enables the researchers to identify and sort males from females. Why is this useful? The ability to rapidly sort mosquitoes by sex makes it possible to produce populations of sterile males and then release the sterile males without the risk of releasing additional females. The release of sterile males may be an effective means of controlling mosquito populations because females breed only once before they die. Mating with a sterile male prevents a female from producing offspring. In 2008, Osamu Shimomura, Martin Chalfie, and Roger Tsien received the Nobel Prize in chemistry for the discovery and the development of GFP, which has become a widely used tool in biology. Overall, as we move forward in the twenty-first century, the excitement level in the field of genetics is high, perhaps higher than it has ever been. Nevertheless, the excitement generated by new genetic knowledge and technologies will also create many ethical and societal challenges. In this chapter, we begin with an overview of genetics and then explore the various fields of genetics and their experimental approaches.
Content
- Reproduction and Chromosome Transmission
- Mendelian Inheritance
- Sex Determination and Sex Chromosomes
- Extensions of Mendelian Inheritance
- Extranuclear Inheritance, Imprinting, and Maternal Effect
- Genetic Linkage and Mapping in Eukaryotes
- Variation in Chromosome Structure and Number
- Genetics of Bacteria
- Genetics of Viruses
- Molecular Structure of DNA and RNA
- Molecular Structure and Organization of Chromosomes
- DNA Replication and Recombination
- Gene Transcription and RNA Modification
- Translation of mRNA
- Gene Regulation in Bacteria
- Gene Regulation in Eukaryotes
- Gene Mutation and DNA Repair
- Recombinant DNA Technology
- Biotechnology
- Genomics I: Analysis of DNA and Transposable Elements
- Genomics II: Functional Genomics, Proteomics, and Bioinformatics
- Medical Genetics and Cancer
- Developmental Genetics and Immunogenetics
- Population Genetics
- Quantitative Genetics
- Evolutionary Genetics
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