The occurrence and inheritance of protein variation in plaice, Pleuronectes platessa L.

Thompson, David (1980). The occurrence and inheritance of protein variation in plaice, Pleuronectes platessa L. PhD thesis The Open University.



The occurrence and inheritance of enzyme polymorphism at eight loci in the plaice, Pleuronectes. platessa, were examined by starch-gel electrophoresis. The enzymes studied were glycerol-3-phosphate dehydrogenase, malate dehydrogenase phosphoglucomutase, glucose phosphate isomerase A and B, 6-phosphogluconate dehydrogenase, iso-citrate dehydrogenase and adenosine deaminase. Conventional crosses demonstrated the codominant genetic control of polymorphism at these loci. The first five enzymes listed above were used in examinations of broods of induced diploid gynogenetic offspring produced from heterozygous females. The results showed that diploidy was caused by the interruption of meiosis in the developing egg and the retention of the second polar body. Recombination frequencies were used to determine the efficiency of induced diploid gynogenesis in the development of inbred lines; these may be of use in the genetical improvement of commercial fish cultivation. The examination of these same inherited enzyme polymorphisms in induced triploid crosses both confirmed the recombination data and also the triploid nature of the offspring. The production of such triploids, if sterile, could increase the yield of fish farming. Throughout the study the results were examined for evidence of selection and linkage apart from some evidence of selection at the glucose phosphate isomerase-A locus no other examples of either phenomenon were observed. Individual anomalous results, when contamination between broods had been discounted, were interpreted as mutations. The occurrence of polymorphism at the eight loci was examined in samples from different spawning grounds in the North Sea, the Irish Sea and off Iceland. Eggs were collected and returned to the laboratory for incubation; the resulting larvae were reared to a size suitable for electrophoresis. The results showed that, with respect to these eight loci, the plaice stocks around the United Kingdom appear to be genetically indistinct but differ from those at Iceland at the glycerol-3~phosphate dehydrogenase, phosphoglucomutase and glucose phosphate isomerase-B loci.

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