Progeny-testing of full-sibs IBD in a SSC2 QTL region highlights epistatic interactions for fatness traits in pigs.
BACKGROUND
Many QTL have been detected in pigs, but very few of them have been fine-mapped up to the causal mutation. On SSC2, the IGF2-intron3-G3072A mutation has been described as the causative polymorphism for a QTL underlying muscle mass and backfat deposition, but further studies have demonstrated that at least one additional QTL should segregate downstream of this mutation. A marker-assisted backcrossing design was set up in order to confirm the segregation of this second locus, reduce its confidence interval and better understand its mode of segregation.


RESULTS
Five recombinant full-sibs, with genotype G/G at the IGF2 mutation, were progeny-tested. Only two of them displayed significant QTL for fatness traits although four inherited the same paternal and maternal chromosomes, thus exhibiting the same haplotypic contrast in the QTL region. The hypothesis of an interaction with another region in the genome was proposed to explain these discrepancies and after a genome scan, four different regions were retained as potential interacting regions with the SSC2 QTL. A candidate interacting region on SSC13 was confirmed by the analysis of an F2 pedigree, and in the backcross pedigree one haplotype in this region was found to mask the SSC2 QTL effect.


CONCLUSIONS
Assuming the hypothesis of interactions with other chromosomal regions, the QTL could be unambiguously mapped to a 30 cM region delimited by recombination points. The marker-assisted backcrossing design was successfully used to confirm the segregation of a QTL on SSC2 and, because full-sibs that inherited the same alleles from their two parents were analysed, the detection of epistatic interactions could be performed between alleles and not between breeds as usually done with the traditional Line-Cross model. Additional analyses of other recombinant sires should provide more information to further improve the fine-mapping of this locus, and confirm or deny the interaction identified between chromosomes 2 and 13.
INRA, UMR Laboratoire de Génétique Cellulaire, Castanet-Tolosan, France. flavie.tortereau@toulouse.inra.fr
Flavie
F
Tortereau
Marie-Pierre
MP
Sanchez
Katia
K
Fève
Hélène
H
Gilbert
Nathalie
N
Iannuccelli
Yvon
Y
Billon
Denis
D
Milan
Jean-Pierre
JP
Bidanel
Juliette
J
Riquet
D000123:Acetyltransferases / Q000235:genetics; D000273:Adipose Tissue; D000818:Animals; D001947:Breeding; D002874:Chromosome Mapping; D000081031:Fatty Acid Elongases; D005260:Female; D005819:Genetic Markers; D006239:Haplotypes; D007178:Inbreeding; D007335:Insulin-Like Growth Factor II / Q000235:genetics; D008297:Male; D008460:Meat; D018895:Microsatellite Repeats; D010375:Pedigree; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide; D040641:Quantitative Trait Loci; D019655:Quantitative Trait, Heritable; D013552:Swine / Q000235:genetics*
D005819:Genetic Markers; D007335:Insulin-Like Growth Factor II; D000123:Acetyltransferases; D000081031:Fatty Acid Elongases