Isoenzyme polymorphism of the sorbitol dehydrogenase and the NADP‐dependent isocitrate dehydrogenases in the fish family Cyprinidae

Among members of the fish family Cyprinidae, the existence of a diploid‐tetraploid relationship is well established. The analysis of individual gene loci, using isoenzyme polymorphism as genetic markers, does not always confirm the expected gene duplication in the tetraploids. Of the markers used in this study, only the M‐form of the NADP‐dependent isocitrate dehydrogenase follows this expectation; the data suggest the existence of a single gene locus for the enzyme in diploids, while the observations on tetraploids were consistent with control by two distinct loci. For two other enzymes, the S‐form of the NADP‐dependent isocitrate dehydrogenase and sorbitol dehydrogenase, no difference seems to exist in the number of gene loci between diploids and tetraploids. A comparison between Cyprinid fish (order Ostariophysi) and members of the order Isospondyli in which another diploid‐tetraploid relationship was established, reveals that gene duplications are more frequently demonstrable within tetraploid Isospondyli than in tetraploid Cyprinidae. From this, it is concluded that polyploidization occurred earlier in evolution of Cyprinidae than of Isospondyli.