Recent developments in molecular and statistical methods have made it possible to identify the genetic basis of any biological trait and have given rise to spectacular advances in the study of human disease. The book provides an overview of the concepts and methods needed to understand the genetic basis of biological traits, including disease, in humans. Using examples of qualitative and quantitative phenotypes, Professor Weiss shows how genetic variation may be quantified, and how relationships between genotype and phenotype may be inferred. The methods for segregation analysis and linkage mapping in human family data are reviewed, and related to standard epidemiological measures of causation and association. In addition, the effects of environmental risk factors are discussed in the context of causal statistical models. Special samples and strategies for identifying genetic variation associated with disease are also examined, and explored from an evolutionary perspective. This book will appeal to a wide range of biologists and biological anthropologists interested in the genetic basis of biological traits, as well as to epidemiologists, biomedical scientists, human geneticists and molecular biologists.