title: Refined positioning of a quantitative trait locus affecting somatic cell score on chromosome 18 in the German Holstein using linkage disequilibrium.
abstract: Combined linkage and linkage disequilibrium analysis (LALD) was conducted to more accurately map a previously reported quantitative trait locus (QTL) affecting somatic cell score on bovine chromosome 18. A grand-daughter design consisting of 6 German Holstein grandsire families with 1,054 progeny-tested genotyped sons was used in this study. Twenty microsatellite markers, 5 single nucleotide polymorphisms, and an erythrocyte antigen marker with an average marker spacing of 1.95 cM were analyzed along a chromosomal segment of 50.80 cM. Variance components were estimated and restricted maximum likelihood test statistics were calculated at the midpoint of each marker interval. The test statistics calculated in single-QTL linkage analysis exceeded the genome-wide significance threshold at several putative QTL positions. Using LALD, we were successful in assigning a genome-wide significant QTL to a confidence interval of 10.8 cM between the markers ILSTS002 and BMS833. The QTL in this marker interval was estimated to be responsible for between 5.89 and 13.86% of the genetic variation in somatic cell score. In contrast to the single-QTL linkage analysis model, LALD analyses with a 2-QTL model confirmed the position of one QTL, but gave no conclusive evidence for the existence or position of a second QTL. Ultimately, the QTL position was narrowed down considerably compared with previous results with a refined confidence interval of less than 11 cM.
authors.affiliation: Forschungsinstitut für die Biologie Landwirtschaftlicher Nutztiere, 18196 Dummerstorf, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Baes
authors.forename: B
authors.initials: B
authors.lastname: Brand
authors.forename: M
authors.initials: M
authors.lastname: Mayer
authors.forename: C
authors.initials: C
authors.lastname: Kühn
authors.forename: Z
authors.initials: Z
authors.lastname: Liu
authors.forename: F
authors.initials: F
authors.lastname: Reinhardt
authors.forename: N
authors.initials: N
authors.lastname: Reinsch
mesh_terms: D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000235:genetics*; D002874:Chromosome Mapping / Q000662:veterinary*; D002875:Chromosomes; D005260:Female; D015810:Linkage Disequilibrium; D008297:Male; D008413:Mastitis / Q000235:genetics / Q000662:veterinary*; D008892:Milk / Q000166:cytology*; D040641:Quantitative Trait Loci / Q000235:genetics*