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Tuesday, 15 January 2008

The use of marker assisted selection to increase disease resistance is a strategy that has the potential to enhance genetic progress with breeding for increased disease resistance (R?ed et al. 1992). Numerous studies on genetic variation in immune response in fish suggest that certain immune parameters may have some potential as practical markers for disease resistance (Balfry et al. 1994, Fevolden et al. 1994; Lund et al., 1995a, 1995b; Wiergertjes, et al, 1995. Specific (humoral antibody and antibody producing cells) and non-specific (lysozyme, macrophage function, blood cell counts) immune parameters may indicate disease resistance to viral or bacterial pathogens can be measured directly. Other genes can be identified using a proteomic approach. Comparison of protein expression in healthy and diseased tissue can pinpoint, which of the thousands of proteins are more or less active at any one time. This will lead to an understanding of the molecular basis of disease. Therefore characterising proteins and understanding their function is important to understand the disease process and may also assist in identifying specific molecules that are involved in disease resistance. These may be molecules involved in the immune response to infection or other stressors. DIGE is the method best suited to this task, involving a comparison of the spots produced in 2 dimensional electrophoresis of serum/plasma for healthy and disease fish. Spot analyses can then identify specific molecules.

Application of new technologies in common carp
In common carp we do not as yet have all of the genetic tools that will enable us to apply these techniques directly. Currently genetic maps based on markers are being developed for several species of commercial interest. In common carp we have a recent first generation low density linkage map from haploid gynogenetic offspring (Sun and Liang 2004) based on 110 microsatellite loci, 105 gene markers and 57 RAPD markers resulted in 50 linkage groups and a total map length of 4111cM. The carp haploid genome is large (n =50) and has been through a relatively recent allotetraploidisation (<12 MYA) David et al. 2003). The map itself is unusual in that nearly all the map distances between genes appear to be equal and there appears to be no evidence for gene duplication. There is a need for a second generation diploid map that will have more practical applications that will include phenotypic traits that will have commercial value and applications in QTL and eQTL approaches in the future.

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