Siegel Review Journal of Heredity 190: 256-257.

Selected Highlights:

Lynch and Walsh deserve thanks for an excellent job of bringing together the multitude of venues used to study quantitative traits. They have successfully integrated approaches and provided a valuable resource to individuals studying quantitative traits. This volume will be much used.

Complete Review

Paul Siegel, Virginia Polytechnic Institute

Receipt of Genetics and Analysis of Quantitative Traits for review brought to mind that almost 40 years have passed since my reviewing of Falconer's (1960) Quantitative Genetics. These four decades have seen dramatic advanced facilitated, in part, by development of computer and molecular technologies and a greater awareness of the field by scientists other than plant and anima breeders. Subtleties also occurred. Whereas my generation credited Fisher, Wright, and Haldane with establishment of the basis of quantitative genetics, Haldane's contributions for establishment of the field have been largely ignored in the preface and initial overview chapter of this volume.

This review is on volume 1, in which the authors state "we have spent 10 years writing a treatise on the subject!" I believe them. They also state that there will be a volume 2, Evolution and Selection of Quantitative Traits, which I look forward to reading. Their description of the present volumes is "we have tried to write a book in a way that will encourage its use as a textbook in quantitative genetics. But the book also provides through enough coverage of the literature so that it should be useful as a basic reference." They have succeeded.

There are three major sections which provide comprehensive coverage of both the "old" and the "new" in quantitative genetics. Eleven chapters are devoted to foundations of quantitative genetics. This section is followed by one on quantitative trait loci (QTL), with a final section on procedures. Then there are more than 80 pages outlining techniques with numerical examples, a satisfactory literature cited list, an adequate author index, a very helpful subject index, and an organism and trait index which in some cases is a shopping list in tabular form. These latter listing are a must in an age of computer indexing for a volume that has a basic reference as one of its objectives.

The following is an outline and brief discussion of the first of the three major sections. Chapter 1, which provides a brief, balanced, and lucid overview of quantitative genetics, is followed by elementary statistical concepts (Chapters 2 and 3). Chapter 4 consists of a discussion of the multidimensional properties of single loci, a topic difficult to explain to undergraduate students. Genetic and environmental variation are topics for Chapters 5 and 6. Included at the end of the latter is a brief explanation of genotype by environment interactions, a topic covered mainly in Chapter 22. The basis for procedures for estimating genetic and environmental variation (resemblance between relatives), as well as shortcoming and nuances of the procedures, are covered in Chapter 7. Chapters 5, 6, and 7 include coverage of haploid, diploid, and polyploid organisms and the role of epistasis, particularly in haploids where dominance does not contribute to nonadditive genetic variation. Also included is a section on genetic disequilibrium and stabilizing selection, as well as bilateral asymmetries.

Chapter 8 consists of an introduction to linear models, matrix algebra, and multivariate concepts. The authors correctly state that this chapter contains "little new" to those with statistical backgrounds.

Line crossing (Chapter 9) and inbreeding (Chapter 10) are interdependent as they address similarities and dissimilarities of within and among population variation. Linkage, recombination, dominance, epistasis, and additivity are discussed. Includes are insights into the genetic architecture of traits not only of interest to plant and animal breeders, but also evolutionary biologists. The final chapter of this section is a potpourri of caveats and conundrums pertaining to what the authors title "matters of scale."

The complex interface of the molecular and statistical story of QTL is encapsulated in the second major section of this volume. There is a transition from viewing traits as influenced by many loci of essentially equal small effects to consideration where genic effects are not only unequal, but where some loci have large qualitative effects. Question posed include, Does most of the expressed variation result from DNA sequence variation in coding regions or to nontranscribed regulatory regions? How much quantitative trait variation is a consequence of variation in timing versus magnitude of gene expression? To what extent are the genes underlying the expression of a quantitative trait present in redundant sets that compliment and/or replace each other? The concept of associations between major genes and polygenic effects is not new, what is recent is that to address these questions requires a marriage between molecular and statistical approaches in the study of genetic variation.

Much research on quantitative traits involves model building, developing indices, measuring distributions, and data manipulation. The statistics are complex and there is need for biological verification to insure against false positives. Chapter 14 is mainly a chronology of the basics for marker-based mapping. This approach is good because it led the reader to the advent of evaluating variation at the DNA level in the mid-1980s. Techniques are quickly outdated and the development of genetic maps has allowed for comparative mapping of QTL across species due to conservation of homologous genes.

Although procedures differ and multiple tests are needed, designs for estimating the genetic architecture of quantitative traits (Chapters 9 and 10) have application in QTL analysis (Chapter 15). The authors are conservative in cautioning readers about difficulties such as false positive, dealing with multiple QTLs, and sample sizes. They provide examples from studies involving tomatoes maize, and mice, and succeed in integrating in an even-handed way information from evolutionary biology, human genetics, and plant and animal breeding.

The third section of this volume, in which there is some redundancy with other parts, provides a comprehensive and up-to-date methodology used in analysis of quantitative traits. There is a coverage of techniques for partitioning genetic variances and covariances (Chapters 17-21) and advantages for the use of maximum likelihood and restricted maximum likelihood estimates (Chapter 27). A lucid presentation of genotype x environment interactions (Chapter 22) is followed by procedures for quantifying maternal effects, sex linkage, sexual dimorphism, threshold traits, and breeding values (Chapters 23-26). To have these procedures in one place is very convenient.

Lynch and Walsh deserve thanks for an excellent job of bringing together the multitude of venues used to study quantitative traits. They have successfully integrated approaches and provided a valuable resource to individuals studying quantitative traits. This volume will be much used.