ISOZYME EXPRESSION AND GENE-CENTROMERE DISTANCES IN DIPLOID AND TRIPLOID HYBRID CATFISH

Allozyme expression of 14 loci was studied in diploid channel catfish Ictalurus punctatus, blue catfish I. furcatus, and diploid and triploi d hybrid catfish (channel catfish X blue catfish). This allowed approp riate interpretation of allozyme expression and estimates of gene-cent romere distances in triploid hybrid catfish and contributed to genetic characterization of the commercially important ictalurid catfishes. F ive polymorphic loci in the parental female channel catfish were used to confirm the retention of an extra diagnostic maternal allele in tri ploid offspring. Fidelity of gene dosage and allozyme expression of th ree parental alleles were found at 13 of 14 loci of triploid progeny; however, expression of phosphoglucomutase (PGM) in 174 and 197 triploi d hybrids was similar to that of diploid hybrids. Electrophoretic vari ation for PGM was observed when different buffers were used, indicatin g nongenetic alteration of expression. Two polymorphic loci in triploi d hybrid catfish provided new gene-centromere distances of 14 centimor gans (cM) for aspartate aminotransferase (mAAT) and 45 cM for glucose -6-phosphate isomerase (GPI-A). No differences were found in recombin ation rates of isocitrate dehydrogenase (IDHP) and peptidase-5 (PEPS- l) loci of triploid hybrids at different ages.