Population Genetics

by

Rob Kulathinal

Introduction

Population genetics is the study of genetic variation, or allele frequencies, across space and time. The patterns observed among alleles within a population are caused by an interplay of evolutionary forces that includes mutation, migration, selection, and drift. Population geneticists study how these forces change both the genotypic and phenotypic makeup of natural populations, using a variety of empirical and theoretical methods. The field of population genetics originated almost a century ago. Initial attempts to integrate Mendelian genetics with Darwin’s theory of natural selection were difficult due to opposing prevailing viewpoints. Early Mendelians did not perceive the continuous nature of small-effect mutational changes and, thus, did not appreciate the gradualism that neo-Darwinians espoused through natural selection. On the other hand, naturalists, particularly biometricians, did not appreciate the laws of inheritance in discrete Mendelian traits, since much of their world revolved around continuously distributed phenotypic traits. A reconciliation between these diverse perspectives was finally made, and population genetic theory went through an initial phase of rapid development, led primarily by three individuals—Ronald A. Fisher, Sewall Wright, and J. B. S. Haldane—who began to form, independently, its mathematical basis. During this classical phase, the structure of DNA was unknown, and molecular techniques that enabled the evaluation of genetic diversity at the nucleotide level were unavailable; however, much progress was made in understanding allele frequency behavior. When population geneticists began to employ molecular techniques in the 1960s, the field shifted from a predominantly theoretical one to an empirical and applied one. New data from molecular population genetics began to challenge many existing paradigms and provided biologists with a new lens to view the world. Today, the scope of population genetics ranges from ecological modeling to medical genetics to speciation genomics. While population geneticists are still interested in understanding how genetic variation is formed, maintained, and transformed, they are employing an increasingly large arsenal of tools and resources, including sequences of entire genomes.

General Overviews

The works in this section provide foundational overviews that are important for understanding the development of population genetics as a field. Provine 1971 is a historical account of the early history of population genetics that presents a unique perspective of the problems that population geneticists first had to solve. Dobzhansky 1951 is a treatise that was instrumental in integrating both an empirical and theoretical population genetics framework into our understanding of evolutionary change, initiating the Modern Evolutionary Synthesis. Three works published in the early to mid-1970s highlight different perspectives of the scope of population genetics theory: Kimura and Ohta 1971 focuses on neutral and nearly neutral trajectories of evolutionary change; Nei 1975 provides a theoretical basis that extends our understanding of evolutionary forces, particularly mutation, from the population level to between-species divergence; and Lewontin 1974 uses a population and quantitative genetics approach to understand what drives evolutionary change. Lewontin writes an excellent overview of basic population and quantitative genetics in the last two chapters of Suzuki, et al. 1989, which is a textbook used by many colleges and universities in introductory genetics classes. More-advanced readers should peruse the diverse collection of thirty-two chapters from Singh and Krimbas 2000, an edited volume on evolutionary genetics.

• Dobzhansky, Theodosius. 1951. Genetics and the origin of species. 3d ed. New York: Columbia Univ. Press.

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  This edition, along with its first edition (1937), is a historically important and influential account describing the relevance of basic population genetic principles to evolution. Although its examples are dated, it is very accessible and not formula heavy.

• Kimura, Motoo, and Tomoko Ohta. 1971. Theoretical aspects of population genetics. Princeton, NJ: Princeton Univ. Press.

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  An important treatise, meant for advanced learning of stochastic changes in populations.

• Lewontin, Richard C. 1974. The genetic basis of evolutionary change. New York: Columbia Univ. Press.

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  A clear description of the molecular data amassed during the dawn of molecular population genetics. Clarifies what these data mean to our understanding of evolutionary processes.

• Nei, Masatoshi. 1975. Molecular population genetics and evolution. New York: American Elsevier.

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  A more or less neutralist view of evolutionary genetics, with an effective treatment of molecular evolution.

• Provine, William B. 1971. The origins of theoretical population genetics. Chicago: Univ. of Chicago Press.

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  An easy-to-read account of the people and the concepts behind the often-contentious beginnings of early population genetics theory.

• Singh, Rama S., and Costas B. Krimbas. 2000. Evolutionary genetics: From molecules to morphology. Cambridge, UK: Cambridge Univ. Press.

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  One of three large, multichapter volumes edited by Singh and Krimbas as part of a festschrift for Richard Lewontin, this book presents an interesting series of articles from leading figures in the population genetics field.

• Suzuki, David T., Anthony J. F. Griffiths, Jeffrey H. Miller, and Richard C. Lewontin. 1989. An introduction to genetic analysis. 4th ed. New York: W. H. Freeman.

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  In this introductory genetics textbook, the final two chapters on population and quantitative genetics provide a clearly written overview of these subjects.