Molecular characterisation of QTLs controlling fatness in pigs

This thesis deals with the identification of genes controlling intramuscular fat and backfat thickness. Markers linked to quantitative trait loci (QTL) for these traits in the cross between Meishan x Large White breeds will lead to the identification of the underlying genetic causes. A whole-genome scan revealed significant evidence for five QTLs affecting body composition, of which four were imprinted. Additional markers were typed in this cross to further investigate the regions on pig chromosome (SSC) 2, SSC4 and SSC7. Imprinting analysis revealed a genome wise significant paternally expressed QTL on SSC2. A radiation hybrid (RH) map was constructed for SSC2. Comparison of the porcine RH map with homologous human chromosomes identified four conserved segments between SSC2 and HSA11, HSA19, and HSA5. To improve the existing comparative map for SSC2 and increase the gene density on this chromosome, a porcine BAC library was screened. Sequences from the BACs were compared with sequences in the nucleotide databases to identify homology with other mammalian sequences. For the investigation of the borders of the conserved segments between SSC2 and HSA11 genes located on HSA11 were mapped to SSC2. This resulted in refinement of the borders of the conserved segments and in the detection of a new rearrangement in the comparative map between HSA11 with the porcine genome. Through the use of radiation hybrid maps that include both Type I and II markers, homologous chromosomal locations for QTL of specific traits can be identified in other species. The conservation of genome organisation between pig, man and mouse makes it possible to take advantage of genetically well-characterised species for the selection of candidate genes for the imprinted QTL for backfat thickness on SSC2. Human obesity research can help to determine the direction and give clues for further porcine fat trait related genetic research, but emphasis should be on better understanding of the fat traits in p