PERFORMANCE TRAITS-LINKED DNA MARKERS AND MARKER-ASSISTED SELECTION

Department of Fisheries and Allied Aquacultures, and Program of Cell and Molecular Biosciences, 203 Swingle Hall, Auburn University, Auburn, AL 36849

Genomics research has two ultimate applied goals: to isolate and clone genes of economic importance for biotechnology and gene-assisted selection (GAS), and to locate and use markers for marker-assisted selection (MAS) in selective breeding programs. To this end, we have identified linked markers for feed conversion efficiency, growth rate, and disease resistance to enteric septisemia of catfish (ESC). Catfish produce large numbers of eggs that allow for the application of phenotypic selective pressure, which produces phenotypically contrasting groups of fish. Selective genotyping was adopted to reduce the amount of genotyping. Three microsatellite markers were identified to be linked to feed conversion efficiency since the best and worst feed converters exhibited drastically different genotypes at three loci of over 100 microsatellite loci tested. Similarly, one marker each was identified to be linked to growth rate and resistance to ESC. The marker linked to growth rate is one of the three markers linked to feed conversion efficiency, consistent with the notion that growth rate and feed conversion efficiency are correlated traits in catfish. This also demonstrates, for the first time at the molecular level, that the QTL for growth and the QTL for feed conversion efficiency may either be the same or located in the same chromosomal region in the catfish genome. Not all the genotypes correlate with the phenotype groups. Theoretically, there are two possible reasons for this: recombination fraction and errors in phenotypic evaluation. The more distant the linked marker is to the QTL controlling the phenotype, the greater the recombination fraction should be. On phenotypic evaluation, certain traits such as growth rate can be accurately evaluated by body weight evaluation, while other traits such as disease resistance can be quite complex. Experience in phenotype and genotype analysis for linked markers will be discussed. The linked DNA markers will be highly useful for MAS programs, and for directing further efforts of genomic mapping for important quantitative traits. An AFLP-based genetic linkage map has been constructed in our laboratory. Mapping of the linked markers to the map is underway.