The discovery in the late 1940's that sickle cell anemia is a "molecular disease" of hemoglobin was the crucial advance that gave birth to the scientific discipline of human molecular genetics. In subsequent years, with the continued expansion of knowledge about the biology and genetics of the hemoglobins, and particularly as a result of the characterization of the very large numbers of globin gene mutations, the human hemoglobin system has remained as the premier model of gene expression at the molecular level in man. With the recent explosion of new information about the genetic properties...