SEX LINKAGE AND NON-MENDELIAN SEGREGATION OF MICROSATELLITE DNA MARKERS IN A MEIOGENETIC FAMILY AND DOMESTIC STRAINS OF TILAPIA (Oreochromis aureus and O. niloticus)

¹ Institute of Animal Science, Agricultural Research Organization, P.O. Box 6, Bet Dagan 50250, Israel

² Laboratory of Fish Immunology and Genetics, Department of Life Sciences, Bar Ilan University, Ramat Gan 52900, Israel

We genotyped using microsatellite markers a family of 33 Oreochromis aureus progeny produced from three meiogenetic siblings (2 females and one male) and the broodstock from which the gynogenetic line was derived. Meiogenesis caused an average of 50% reduction in polymorphic loci among the three gynogens. We identified a significant association (P = 0.003) between one marker (UNH160) and sex determination in the broodstock (N = 30). The parental allele of UNH160 could not be detected in the progeny of the gynogenetic family. Matings to produce informative families from the broodstock are currently underway. A highly significant deviation from the expected mendelian segregation was also identified in the markers UNH111, 159 and 216. Genotypes of O. aureus and O. niloticus haploids and full-sib O. niloticus x O. aureus backcrosses suggest that UNH111 represents a duplicated locus in the two domesticated O. aureus strains examined and may have three copies in the haploid genome of our O. niloticus strain. Preliminary sequence comparison of UNH111 PCR amplified fragments suggests that size differences were caused by changes in the regions flanking the CA repeat and not by changes in the repeat motif itself. Analysis of O. aureus x red O. niloticus F₂ hybrids should enable estimation of genetic linkage between the putative UNH111 loci and is currently underway. The frequency of UNH159 heterozygotes (88%) is significantly higher (P = 0.00002) than expected by mendelian segregation in the gynogenetic family. One of the two UNH216 alleles (117 bp) detected in our O. aureus population is only present in the heterozygous form. We designed matings to test for linkage of both UNH159 and UNH216 to loci with lethal alleles.