POLYMORPHISMS, LINKAGE AND MAPPING OF FOUR ENZYME LOCI IN THE FISH GENUS XIPHOPHORUS (POECILIIDAE)

Donald C. Morizot ¹ and Michael J. Siciliano ²

¹ The University of Texas Graduate School of Biomedical Sciences
² Department of Biology, The University of Texas System Cancer Center, M. D. Anderson Hospital and Tumor Institute, Houston, Texas 77030

Electrophoretic variants at four additional enzyme loci—two esterases (Est-2, Est-3), retinal lactate dehydrogenase (LDH-1) and mannose phosphate isomerase (MPI)—among three species and four subspecies of fish of the genus Xiphophorus were observed. Electrophoretic patterns in F₁ hybrid heterozygotes confirmed the monomeric structures of MPI and the esterases and the tetrametric structure of LDH in these fishes. Variant alleles of all four loci displayed normal Mendelian segregation in backcross and F₂ hybrids. Recombination data from backcross hybrids mapped with Haldane's mapping function indicate the four loci to be linked as Est-2—0.43—Est-3—0.26—LDH-1—0.19—MPI. Significant interference was detected and apparently concentrated in the Est-3 to MPI region. No significant sex-specific differences in recombination were observed. This group (designated linkage group II) was shown to assort independently from the three loci of linkage group I (adenosine deaminase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase) and from glyceraldehyde-3-phosphate dehydrogenase and two isocitrate dehydrogenase loci. Evidence for conservation of the linkage group, at least in part, in other vertebrate species is presented.