Genetic linkage mapping of allozyme loci in even- and odd-year pink salmon (Oncorhynchus gorbuscha)

Abstract

Genetic linkage maps of allozyme loci were constructed in even- and odd-year pink salmon (Oncorhynchus gorbuscha). The loci were mapped based on the results of gene-centromere (G-C) mapping and joint segregation analysis. For G-C mapping, 160 gynogenetic progeny families were produced, and 8,080 progeny from 74 families were analyzed using starch gel electrophoresis and histochemical stain techniques. G-C distances of 37 loci ranged from 0.5 cM at sMDH-A1* to 50 cM at sMDH-B2*. Eleven loci showed high G-C distances (>45 cM), indicating that one crossover on one chromosome arm is usual in pink salmon. Variation observed at sMDH-B1,2* in even-year families suggests that both of this loci is polymorphic and that there is possible inter-broodline chromosomal variation. Large variation was observed among families in G-C distance at several loci. Whether the variation was a reflection of difference in physical position, recombination rate, or some other factors needs clarification using a technique such as physical mapping with FISH, because this variation affects results of gene mapping based on recombination frequency. For joint segregation analysis, 320 biparental families were produced, and 13,068 progeny from 164 families were electrophoretically analyzed. Joint segregation was analyzed at over 200 locus pairs. Combined this with data from G-C mapping, 14 linkage groups involving 26 loci were constructed. The linkage maps contain eight classical linkage groups and four pseudolinkage groups. Two linkage groups found in pink salmon were conserved in widely divergent vertebrate species. Recombination frequency between linked loci were different between sexes, and it tends to be reduced in males in pink salmon. The order of loci, which probably duplicated in the recent tetraploidization event, in linkage groups I (sAAT-3 * → mAH-4*) and III (mAH-3* → sAAT-4*) was reversed. This is evidence of paracentric inversion during salmonid evolution after the duplication. Development of additional markers that are common (homologous) to many species will be necessary to examine syntenic stability and rearrangement over the evolutionary period.