Eleven full sib families were analysed by means of starch gel electrophoresis or isoelectric focusing in order to verify the genetic control and the mode of inheritance of the polymorphism of 15 enzyme systems. The study includes a check on environmental, ontogenetic and tissue specific variation of isoenzymes with inclusion of in vitro stages and also on the localization of certain enzyme systems within cell compartments. Intra-individual modification of isoenzymes can occur in the systems ACP, EST, and PER, which therefore were not included in the genetic analyses.