GENETIC VARIATION IN NATURAL POPULATIONS: LINKAGE MAPPING OF FITNESS RELATED TRAITS IN SOAY SHEEP
D. Beraldi, J. Gratten, A. F. McRae, P. M. Visscher, J. Slate, J. M. Pemberton
University of Edinburgh
Traits under the pressure of natural selection are expected to lose their genetic variability since the negative
genetic variants are counter-selected and replaced by the positive alleles. However, direct, empirical observations
show that fitness related traits maintain, or even enhance, their genetic variability in the face of selection. One
strategy by which the complexity of continuous characters can be dissected and the loci that contribute to trait
variation identified is linkage mapping. Thanks to previous studies, the Soay sheep on St Kilda, the free-living
population which is the subject of this project, offers an unprecedented opportunity to dissect the architecture of
fitness related traits. In this project, a pedigree of 588 animals was genotyped to build a complete genetic map and a
whole genome scan was carried out to detect loci for qualitative and quantitative traits realted to fitness. The loci
affecting horn type and two aspects of coat colour were mapped: Horn type mapped to chromosome 10, Coat colour
to chromosome 2, Coat pattern to chromosome 13 (LOD scores >3). One genomic region showed significant linkage
with the variation in jaw length (chromosome 11, LOD= 3.59). In addition, suggestive linkages were detected for
hind leg length (chromosome 15, LOD= 2.89), birth weight (chromosome 8, LOD= 2.54), and timing of birth
(chromosome 2, LOD= 2.70). Finally, two suggestive linkages were scored for resistance to the gastrointestinal
parasite coccidia (chromosome 3 and X, LOD= 2.68 and 2.21, respectively). The results reported here will improve
our understanding of the evolution and genetics of natural populations by allowing a more realistic modelling of the
study traits and by opening the way towards the molecular characterization of the genomic regions of interest.
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