Quantitative genetics traces back to Fisher's (1918) synthesis of Mendelian genetics with the biometric analysis of continuous traits. It provides an elegant statistical framework for understanding the relation between phenotype and genotype, and the response of populations to natural and artificial selection. Until recently, this body of theory was confined largely to plant and animal breeding, and even there, only the most elementary aspects were in common use. In the past decade, the availability of fast computers and abundant molecular markers has stimulated sophisticated applications over a wider field, and has again brought together discrete Mendelian genetics with the continuous variety of whole organisms.
Lynch and Walsh set out to combine in a single definitive text the diverse applications of quantitative genetics to plant and animal breeding, human genetics, and evolutionary biology. Genetics and analysis of quantitative traits is the first of what will now be two volumes; the second will cover Evolution and selection of quantitative traits. Despite its broad scope and long gestation, this volume is much lighter than one might expect. In less than 1.5Kg and 1000 pages, it covers the whole field, and succeeds remarkably well in bringing together methods that have been developed in diverse contexts. The explanations of difficult concepts are admirably clear, and should be accessible to those without a strong mathematical background. Methods are derived from first principles, and illustrated by well-chosen worked examples; there are also helpful appendices on basic statistics, matrix algebra, and likelihood. The references are comprehensive, covering both the early literature in which most of the theory was outlined, and the papers of the last few years in which it is elaborated and applied.
The sophisticated and precise theory of quantitative genetics rests on uncertain biological foundations: we have only the barest outline of the genetic basis of continuous variation, and of the evolutionary processes by which it is maintained. Lynch and Walsh give thoughtful summaries of several key issues: for example, mutation; regulatory vs. structural variation; developmental stability; correlations between characters; and phenotypic plasticity. Particularly intriguing is a survey of 52 attempts to detect quantitative trait loci (QTL) using inbred lines, they find for half of all traits, one locus accounts for at least 20% of the phenotypic variance (Ch. 15). However, they also caution that there is a serious statistical bias which leads to overestimation of the effects of detected QTL, and point out that the rapid generation of variation by mutation, and prolonged selection response, are strong evidence for polygenic variation. Overall, this volume will be an indispensable reference for all in the field, and an excellent basis for graduate courses.