| Research Abstract |
Microsatellite markers that we mainly used in this study :
Looking to the future, it is clear that a particular class of nuclear markers, referred to as short tandem repeats (STR or microsatellites), may maximize cost : benefit ratio for most aquatic selective breeding programs. Besides a large abundance throughout the genome of a target species, microsatellites exhibit high levels of allelic variation. This means that microsatellites confer more information per unit assay than other marker systems.
Range capable of microsatellite markers :
We confirmed the range capable of microsatellite markers islated from rainbow trout or Japanese flounder. As a result, microsatellite markers are able to be used in the level of genus, although all microsatellite markers not always fit to the tested fishes.
Genetic linkage map :
(1) Japanese flounder
We made the first genetic linkage map of the Japanese flounder Paralichthys olivaceus ) constructed with 111 microsatellite markers and 352 AFLP fragments. T
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he parental male linkage map consisted of 25 linkegae groups while the female map consisted of 27 groups, with an average resolution of 8 cM and 6.6 cM, respectively. We have identified linkage among 96 % of the markers and the total map length was estimated to be around 1000-1200 cM.
(2) Rainbow trout
We constructed a genetic linkage map for a tetraploid derivative species, the rainbow trout (Oncorhynchus mykiss), using 190 microsatellite, 3 RAPD, 7 ESMP, and 7 allozyme markers in three backcross families. The linkage map consists of 29 linkage groups with potential arm displacements in the female map due to male-specific pseudolinkage arrangements. Females had much lower recombination rates (0.41:1) in telomeric regions than males, while recombination rates were much higher in females within regions proximal to the centromere (F:M = 10:1).
QTL analysis for IPN disease resistance in rainbow trout :
Infectious pancreatic necrosis (IPN) is a highly contagious viral disease which causes excessive mortality among salmonid fish. Rainbow trout genetic likage maps we constracted has made possible the identification of individual loci controlling quantitative traits such as disease resistance. We mapped quantitative trat loci (QTLs) for IPN resistance in a segregated polulation of backcross derived from out-crossing the resistant strain of rainbow trout, RT-201 and the susceptible one, RT-101.
Phenotypic scores of 1-dead/susceptible and 0-survivor/resistant for QTL analysis were recorded from the results of artificially induced infection with IPNV. QTL analysis was carried out using a framework likage map based on microsatellite markers and a software, Map Manager QT. Two putative QTLs (IPN R/S-1 and -2) affecting disease resistance were detected on Chromosomes A and C designated by Sakamoto et al., suggesting that this trait is polygenic in rainbow trout. This is the first report of the identification of QTLs associated with disease resistance in fish. Less
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