Expression of the paternally derived phosphoglucose isomerase genes during hybrid trout development

Abstract 1. 1. Salmo trutta and Salvelinus fontinalis (Salmonidae: Isospondyli) have distinct electrophoretic phosphoglucose isomerase (PGI) phenotypes. 2. 2. Embryos resulting from intraspecific and interspecific matings of these 2 species were analysed for the development of the electrophoretic PGI patterns, the total PGI activity, and the total soluble protein content. 3. 3. Embryonally encoded PGI is demonstrable comparatively early in development (Witschi stage 18). 4. 4. In the interspecific hybrids the activation of one species specific PGI locus depends on whether it is introduced by the mother or by the father. This finding is discussed in terms of the evolutionary origin of this gene and in view of the hypothesis that the expression of genes may be modulated by variability of receptor sequences adjacent to structural genes. 5. 5. Total PGI-activity and soluble protein content during embryonic development are quantitatively fixed to the maternal species.