Genetic linkage maps consist of ordering molecular markers across the genome and require a high number of markers for a good coverage of the genome. Such maps represent a framework which enables the identification and localisation of Quantitative Trait Loci (QTLs) for traits of interest, such as growth or disease resistance, with the final aim of achieving genetic improvement through marker-assisted selection (MAS). Data on bivalves are scarce. No genetic map has yet been constructed in any mussel or flat oyster species.
We report construction of a preliminary genetic linkage map in the blue mussel, Mytilus edulis (n=14). Amplified Fragment Length Polymorphism (AFLP) markers were used in a mapping family containing 86 full-sibs issued from a controlled pair mating, applying a double
pseudo-test cross strategy. Sex-specific linkage maps consisting of 14 linkage groups were built with MapMaker 3.0 software. In addition, a consensus map was built for 9 homologous pairs based on multiple and parallel linkages of 3:1 markers (segregating through both parents) with JoinMap 4.0 software.
Moreover, the first genetic linkage map for the European flat oyster Ostrea edulis (n=10) is presented. AFLP markers and twenty microsatellites were genotyped in a three-generation pedigree mapping family comprising the 2 grand-parents, 2 parents and 92 progeny. Sex-specific linkage maps were built with CriMap software, achieving an estimated genome coverage of 82-84%. Eight linkage groups that_ were probably homologous between the two parents were
identified by the mapping of microsatellites and 3: 1 AFLPs. Distorted markers were not randomly distributed across the genome and tended to cluster in a few linkage groups.
Finally, we report the finding of several potential QTLs of resistance and susceptibility to bonamiasis (parasitosis due to Bonamia ostreae) in 0. edulis. The experimental set up consisted of a 6-month trial challenge experiment by cohabitation of wild oysters (overinfected with B. ostreae) and tested oysters (two three-generation pedigree segregating families). The disease was
transmitted from the wild oysters to the tested oysters, with the first mortalities in the tested oysters occurring after four months of cohabitation. There was a good concordance in the QTLs obtained with three different methodologies used: multi-stage testing strategy, genetic mapping and QTL mapping with QTL express software. The results, even if preliminary, represent a first
step towards MAS in the flat oyster.