Reflecting the expansion of research in molecular and clinical genetics, and immunogenetics, this dictionary now contains over 6000 definitions, nearly a third of which have been added since the Second Edition. Many of the terms are of recent coinage, especially those from molecular genetics, and other terms, such as those used in quantitative genetics or mutational studies, are from related disciplines. Indeed, this is the only dictionary of genetics to incorporate terms from chemistry, physics, statistics, biochemistry, and medicine that are commonly encountered in the genetic literature.