Hartl, Jones - Genetics. Principlers and analysis - 1998, страница 7

Louis, MOJeffrey King, University of Berne, SwitzerlandK. Brooks Low, Yale UniversityGustavo Maroni, University of North CarolinaJeffrey Mitton, University of Colorado, BoulderGisela Mosig, Vanderbilt UniversityRobert K. Mortimer, University of California, BerkeleyRonald L. Phillips, University of MinnesotaRobert Pruitt, Harvard UniversityPamela Reinagel, California Institute of Technology, PasadenaKenneth E.

Rudd. National Library of MedicineLeslie Smith, National Institute of Environmental Health Sciences, Research Triangle Park,NCJohan H. Stuy, Florida State UniversityIrwin Tessman, Purdue UniversityKenneth E. Weber, University of Southern MaineWe would also like to thank the reviewers, listed below, who reviewed one or more chapters andwho, in several cases, reviewed the complete fourth edition manuscript. Their comments andrecommendations helped improve the content, organization, and presentation of the material. Weoffer special thanks to Dick Morel, who carefully reviewed and commented on all of theillustrations as well as the text.Laura Adamkewicz, George Mason UniversityPeter D.

Ayling, University of Hull (UK)Anna W. Berkovitz, Purdue UniversityJohn Celenza, Boston UniversityStephen J. D'Surney, University of MississippiKathleen Dunn, Boston CollegeDavid W. Francis, University of DelawareMark L. Hammond, Campbell UniversityRichard Imberski, University of MarylandSally A. MacKenzie, Purdue UniversityKevin O'Hare, Imperial College (UK)Peggy Redshaw, Austin CollegeThomas F.

Savage, Oregon State UniversityDavid Shepard, University of DelawareCharles Staben, University of KentuckyDavid T. Sullivan, Syracuse UniversityJames H. Thomas, University of WashingtonWe also wish to acknowledge the superb art, production, and editorial staff who helped make thisbook possible: Mary Hill, Patrick Lane, Andrea Fincke, Judy Hauck, Bonnie Van Slyke, SallySteele, John Woolsey, Brian McKean, Kathryn Twombly, Rich Pirozzi, Mike Campbell, and TomWalker. Much of the credit for the attractiveness and readability of the book should go to them.Thanks also to Jones and Bartlett, the publishers, for the high quality of the book production. We arealso grateful to the many people, acknowledged in the legends of the illustrations, who contributedphotographs, drawings, and micrographs from their own research and publications, especially thosewho provided color photographs for this edition.

Every effort has been made to obtain permission touse copyrighted material and to make full disclosure of its source. We are grateful to the authors,journal editors, and publishers for their cooperation. Any errors or omissions are wholly inadvertantand will be corrected at the first opportunity.Page xxiIntroduction:For the StudentIn signing up for a genetics course, our students often wonder how much work is going to berequired, how much time it will take to do the reading and written assignments, how hard theexaminations will be, and what is their likelihood of getting a good grade. These are perfectlylegitimate issues, and you should not feel guilty if they are foremost in your mind.You may also be wondering what you are going to learn by taking a course in genetics.

Will thematerial be interesting? Is there any reason to study genetics other than to satisfy an academicrequirement? At the end of the course, will you be glad that you took it? Will there be any practicalvalue to what you will learn? This introduction is designed to reassure you that the answer to eachquestion is yes. The study of genetics is relevant not only to biologists but to all members of ourmodern, complex, technological society.

Understanding the principles of genetics will help you tomake informed decisions about numerous matters of political, scientific, and personal concern.At least 4000 years ago in the Caucasus, the Middle East, Egypt, South America, and other parts ofthe world, farmers recognized that they could improve their crops and their animals by selectivebreeding. Their knowledge was based on experience and was very incomplete, but they didrecognize that many features of plants and animals were passed from generation to generation.

Theydiscovered that desirable traits—such as size, speed, and weight of animals—could sometimes becombined by controlled mating and that, in plants, crop yield and resistance to arid conditions couldbe combined by cross-pollination. The ancient breeding programs were not based on much solidinformation because nothing was known about genes or any of the principles of heredity. In a fewinstances, the pattern of hereditary transmission of a human trait came to be recognized. Oneexample is hemophilia, or failure of the blood to clot, which results in life-threatening bleeding fromsmall cuts and bruises.

By the second century of the present era, rules governing exemptions fromcircumcision had been incorporated into the Talmud, indicating that several key features of themode of inheritance of hemophilia were understood. The Talmud's exemptions apply in the case of amother who lost two sons from excessive bleeding following circumcision: Subsequent boys born tothe same mother, and all boys born to her sisters, were exempt. However, the paternal half brothersof a boy who had died from excessive bleeding were not exempt. (Paternal half brothers have thesame father but a different mother.) These rules of exemption from circumcision make very goodsense when judged in light of our modern understanding of the inheritance of hemophilia, as youwill learn in Chapter 3.The scientific study of heredity is called genetics. The modern approach to genetics can be traced tothe mid-nineteenth century with Gregor Mendel's careful analyses of inheritance in peas.

Mendel'sexperiments were simple and direct and brought forth the most significant principles that determinehow traits are passed from one generation to the next. In Chapter 2, you will learn the rules followedby genes and chromosomes as they pass from generation to generation, and you will be able tocalculate in many instances the probabilities by which organisms with particular traits will beproduced. Mendel's kind of experiments, which occupied most of genetic research until the middleof the twentieth century, is called transmission genetics. Some people have called it formalgenetics, because the subject can be understood and the rules clearly seen without any reference tothe biochemical nature of genes or gene products.Beginning about 1900, geneticists began to wonder about a subject we now call molecular genetics.Is the gene a known kind of molecule? How can genetic information be encoded in a molecule?How is the genetic information transmitted from one generation to the next? In what way is thegenetic information changed in a mutant organism? At that time, there was no logical starting pointfor such an investigation, no experimental ''handle." In the 1940s, critical observations were madethat implicated the molecule deoxyribonucleic acid (DNA), first discovered in 1869.

You will learnabout these experiments in Chapter 1. With the discovery of the structure of DNA in 1953 byWatson and Crick, genetics entered the DNA age. Within a decade, there came an understanding ofthe chemical nature of genes and how genetic information is stored, released to a cell, andtransmitted from one generation to the next. During the first three decades after the discovery ofDNA structure, the body of genetic knowledge grew with a two-year doubling time. These wereexciting times, and you will be presented with a distillation of these findings in the chapters of thisbook that deal with molecular genetics.Since the early 1970s, genetics has undergone yet another revolution: the development ofrecombinant DNA technology. This technology is a collection of methods that enable genes to betransferred, at the will of the molecular geneticist, from one organism to another.