SEX-LINKAGE OF GLUCOSEPHOSPHATE ISOMERASE-B AND MAPPING OF THE SEX-DETERMINING GENE IN CHANNEL CATFISH

Sex-linkage of glucosephosphate isomerase-B (GPI-B) was observed in fi ve experimental matings between heterozygous male and homozygous femal e channel catfish (Ictalurus punctatus). Offspring phenotypes for GPI- B were 40.8% heterozygous male and 43.0% homozygous female, while reco mbinant offspring were 7.4% homozygous male and 8.8% heterozygous fema le. Thus, GPT-B and the sex-determining gene (SDG) were Linked and had a recombination rate of 16.2%. This linkage was designated I. punctat us linkage group XXIX. The gene-centromere distance (1.66 cM) of SDG, estimated in six gynogenetic families derived from XY females, indicat ed that SDG resides very close to the centromere. Based on estimates o f these genetic distances, a chromosomal order of GPI-B-centromere-SDG was proposed. Additionally, joint segregation of GPI-A and SDG in two experimental matings indicated no genetic linkage between GPI-A and s ex. These genetic relationships were compared to those reported in oth er teleost taxa with regard to evolutionary conservation of ancestral gene arrangements.