A porcine BAC library with tenfold genome coverage: a resource for physical and genetic map integration

摘要

Recent advances in porcine genomics have identified quantitative trait loci (QTL) that influence pork production traits such as carcass traits, meat quality, and reproductive efficiency (Rohrer 2000; Cassady 1999). The low resolution to which most of these loci have been defined precludes the accurate application of markerassisted selection (MAS) strategies for increasing production efficiency. Large-insert genomic libraries are an excellent resource for marker development aimed at increasing the resolution of QTL and for the development of contiguous physical maps (contigs) of the chromosomal regions containing them. To facilitate applications requiring genomic clones, several porcine yeast artificial chromosome (YAC) libraries have been developed representing onefold (Leeb et al. 1995), threefold (Rogel-Gaillard et al. 1997), and 5.5-fold (Alexander et al. 1997) coverage of the pig genome. These YAC libraries have been valuable resource owing to their large insert size. However, marker isolation from YAC libraries is confounded by the equimolar representation of the complex yeast genome and YAC DNA, susceptibility to insert rearrangement, and a relatively high degree of chimerism. The development of bacterial artificial chromosome (BAC) libraries (Shizuya et al. 1992; Ioannou et al. 1994) represents a compromise between insert size, stability, and ease of clone DNA isolation. BACs are capable of stably maintaining insert sizes exceeding 200 kb and can be easily isolated by standard alkaline lysis from bacterial genomic DNA by virtue of their closed-circular conformation (Shizuya et al. 1992; Ioannou et al. 1994). The ease of BAC DNA isolation allows for efficient restriction analysis, subcloning, and direct BAC DNA sequencing, procedures invaluable for marker isolation and the development of contiguous physical maps.