1 Laboratory of Fish Genetics, INRA, 78352 Jouy-en-Josas, France 2 Department of Zoology,University of Guelph, Guelph, Ontario, Canada N1G 2W1 3 Department of Aquatic Biosciences, Tokyo University of Fisheries, Minato, Tokyo 108, Japan
Comparative mapping in salmonids is of particular interest to investigate (i) chromosomal evolution following ancestral tetraploidization in this fish family and (ii) the opportunity to locate conserved quantitative trait loci (QTLs). Brown trout (Salmo trutta, 2n=77-82, NF=96-102) has fewer metacentric chromosomes than most salmonids and hence favours assignment of linkage groups (LGs) to single chromosome arms which are regarded as the basic units of the salmonid karyotype. Therefore, a comparative linkage map of this species is expected to be of main importance. Fifty nine microsatellite loci isolated from different species of salmonids and previously mapped in rainbow trout (Oncorhynchus mykiss, 2n=58-65, NF=104) were tested in brown trout. A high cross-priming rate of 80% was obtained. Size polymorphism was detected for 70% of these loci in a sample of 55 parents corresponding to 29 intraspecific backcrosses or F2 families and fourteen meiotic gynogenetic lines. Comparative mapping was performed for ten rainbow trout LGs (including two pairs of homeologous ones) involving two to six loci. Joint segregation analyses led to the identification of seven conserved LGs. Marker order and map distances were also highly conserved which is consistent with previous salmonid mapping studies based upon allozymes. Evidence of disrupted linkage was demonstrated in one case. Amplification of non homologous loci could not be excluded for the two other cases. Further investigations, including assessments of gene-centromere distances, are required to clarify this evolutionary breakpoint. Altogether these results show that microsatellites are valuable tools for comparative mapping in salmonids.
Plant & Animal Genome VII Conference Plant & Animal Genome VII Conference