书名：Principles of Population Genetics (3rd edition)
作者：Daniel L. Hartl and Andrew G. Clark
DH: Harvard University
AC: Pennsylvania State University
Preface
Thanks in part to the power of molecular methods, population genetics has been reinvigorated. As some genome projects are approaching closure and methods of “functional genomics” are scaling up to identify the roles of novel genes; inevitably increasing attention is being paid to the significance of genetic variation in populations. Nowhere is this more evident than in medical genetics. Within a decade we can expect that all major single-gene inherited disorders will be identified, genetically mapped, cloned, and characterized at a fine molecular level. Health professional realize that this impressive feat will have an impact only on a small minority of individuals. Most of the genetic variation in disease risk is multifactorial, which means that risk is determined by multiple genetic and environmental factors acting together. Killer diseases such as familial forms of cancer, diabetes, and cardiovascular disease fall into this category. The face that these disease aggregate in families implies that there is probably a genetic component, but the genetic component may differ from one family or ethnic group to another. Prompted by the high incidence of multifactorial diseases as a group, the medical community has become acutely aware of the need to understand the basic structure of genetic variation in populations in order to determine what aspects of the variation cause disease.
The exciting practical applications of population genetics to the analysis of multifactorial diseases have received great attention, but the scope of population genetics actually is much broader. Population genetics provides the genetic underpinning for all of evolutionary biology. By “evolution” we mean descent with modification as they adapt to their environments, and new species arise as a by-product of this process. The intellectual excitement of biological evolution arises from the fact that it addresses the fundamental questions, “hat are we?” and “where did we come from?”
Patterns of evolutionary history are recorded in DNA sequences, and the application of population genetics to interpreting DNA sequences is revealing many secrets about the evolutionary past, including the history of our own species. But population genetics embraces much more than the analysis of evolutionary relationships. It is particularly concerned with the processes and mechanisms by which evolutionary changes are made. The field is inherently multidisciplinary, cutting across molecular biology, systematics, natural history, plant breeding, animal breeding, conservation and wildlife management, human genetics, sociology, anthropology, mathematics, and statistics.
Students taking population genetics are usually expected to have completed, or to be taking concurrently, a course in differential calculus. While this book assumes a familiarity with the elementary notation for differentials and integrals, it does not require great mathematical proficiency. We have kept the mathematics to a minimum. On the other hand, some of the most important models in population genetics require quite advanced mathematics. Rather than ignore these approaches, we have made a concerted effort to present these models in such a way that the assumptions can be understood and the main results appreciated without much mathematics. References are provided for the interested reader to learn more about the details.
Several important changes distinguish the third edition of Principles from the second edition. The level of the treatment is more tailored to the needs of a one-semester or one-quarter course, with the intended audience being third- and forth-year undergraduates as well as beginning graduate students. Population genetics is not only an experimental science but also a theoretical one. Special care has been taken to explain the biological motivation behind the theoretical models so that the models do not simply materialized out of thin air, and to explain in plain English the implications of the results. Many concepts are illustrated by numerical examples, using actual data wherever possible. Special topics and examples are often set off from the text as boxed problems whose solutions are explained step by step. Every chapter ends with about 20 problems, graded in difficulty, and solutions worked in full appear at the end of the text.
This edition of Principles is organized into nine chapters that gradually build concepts from measuring variation and the various forces that influence genetic variation through a sequential progression to concepts from measuring variation and the various forces that influence genetic variation through a sequential progression to concepts of molecular population genetics and quantitative genetics and quantitative genetics. The first chapter provides a background in basic genetic and statistical principles. We discuss the fundamental concepts of allelism, dominance, segregating, recombination, and population frequencies. The role of model building and testing in population genetics is emphasized. Chapter 2 introduces the student to the primary data of population genetics, namely, the many levels of genetic variation. Chapter 3 is concerned with the organization of genetic variation. Chapter 3 is concerned with the organization of genetic variation into genotypes in populations. Here the Hardy-Weinberg principle gets very thorough coverate, including the cases of X-linkage and multiple alleles. Chapter 4
The goal of population genetics is to understand the forces that have an impact on levels of genetic variation. The forces of mutation, recombination, and migration are outlined in Chapter 5. Darwinian selection is the topic of Chapter 6, including both the theoretical foundations and empirical observations of the dynamics of gene-frequency change under the action of selection. Haploid and diploid cases are developed, as are the concepts of equilibrium, stability, and context dependence. After classical models of mutation-selection balance are developed, a series of more complex scenarios of natural selection are presented.
Chapter 7 deals with random genetic drift. In the absence of other forces, allele and genotype frequencies change as result of random sampling from one generation to another. The Wright-Fisher model and diffusion approximations are presented in such a way that the student gains an appreciation for the importance of random genetic drift. The process of the coalescence of genealogies is an important innovation in theoretical population genetics, and some of the basic concepts of coalescence are presented in Chapter 7.
In Chapter 8 we cover the rapidly expanding data on molecular evolutionary genetics. The unifying theme in the study of molecular evolution is Kimura’s neutral theory, and a close examination is make of the correspondence between the data and theory. This is a field in which advances in our empirical database and statistical tools for quantifying and manipulating the data are growing at a dizzying pace. Our goal is to give the student a firm grasp of the fundamentals, and a deep enough understanding of the principles to identify important gaps in our knowledge. One intriguing aspect of molecular evolutionary genetics is the discovery of new phenomena and forces taking place at the molecular level that go beyond the realm of classical population genetics. Multigene families and organelle genomes are described in some detail to illustrate these uniquely molecular phenomena.
Chapter 9 covers the problem of quantitative genetics from an evolutionary perspective. A compelling argument for using quantitative genetics for the study of evolution is that adaptive evolution takes place at the level of the phenotype, and quantitative genetics provides the tools for understanding transmission of phenotypic traits. Theoretical quantitative genetics is given special importance by the paradoxes it raises in contrasting evolution at the levels of the phenotype and of the DNA sequence. Our understanding of the correspondence between phenotypic and molecular differentiation is very incomplete, and our understanding of the correspondence between the rates of morphological and molecular evolution is even less well developed. As in the preceding chapters, we hope that the student is left with a feeling that there is plenty of room for imaginative work in this area. Population genetics is a field with a bright and expanding future.
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