1 Biochemistry and Genetics of the ABO, Lewis, and P Blood Group Systems.- The ABO System.- The Lewis System.- The P System.- Serology and Genetics.- Chemistry of P1, P, and Pk Determinants.- Biosynthetic Pathways.- Relationship between ABH and P Systems.- Concluding Remarks.- References.- 2 HLA—A Central Immunological Agency of Man.- HLA: A Supergene.- HLA Terminology.- Inheritance of HLA.- The HLA-A, -B, and -C Allelic Series of Antigens.- HLA-D.- Cell-Mediated Lympholysis (CML).- HLA-DR.- Population Genetics.- The HLA “Supergene” and Transplantation.- Evolution and Maintenance of the MHC—Function?.- What of the Future?.- References.- 3 Linkage Analysis in Man.- General Considerations.- Historical Perspective.- Approach to Family Studies.- Preparation of Data Prior to Analysis.- Analysis of Data.- Interpretation of Results.- Multipoint Mapping.- Significance of Linkage.- References.- 4 Sister Chromatid Exchanges.- BrdUrd Methodology for SCE Detection.- Basic Information about SCEs.- Induction of Sister Chromatid Exchange by Clastogens.- Extension of SCE Studies from in Vitro to in Vivo Systems.- Interpretation of SCE Induction Tests.- Relationship of SCE Induction to DNA Damage, Repair, and Synthesis.- Relationship of SCE Induction to Mutagenesis.- Sister Chromatid Differentiation in Meiotic Cells.- Sister Chromatid Exchange Formation in Heritable Human Diseases.- Studies of the Mechanism of SCE Formation.- References.- 5 Genetic Disorders of Male Sexual Differentiation.- Normal Male Sex Differentiation in the Fetus.- Abnormal Male Sex Differentiation.- References.- Addenda.