title: Mapping of QTL affecting incidence of blood and meat inclusions in egg layers.
abstract: BACKGROUND
  Occurrence of blood and meat inclusions is an internal egg quality defect. Mass candling reveals most of the spots, but because brown eggshell hampers selection in brown chicken lines it has not been possible to eliminate the defect by selection. Estimated frequency of blood and meat inclusions in brown layers is about 18% whereas it is 0.5% in white egg layers. Several factors are known to increase the incidence of this fault: genetic background, low level of vitamin A and/or D, stress or infections, for instance. To study the genetic background of the defect, a mapping population of 1599 F2 hens from a cross of White Rock and Rhode Island Red lines was set up.
  
  
  RESULTS
  Our histopathological analyses show that blood spots consist of mainly erythrocytes and that meat spots are accumulations of necrotic material. Linkage analysis of 27 chromosomes with 162 microsatellite markers revealed one significant quantitative trait locus (QTL) affecting blood spot and meat spot frequency. We sequenced a fragment of a candidate gene within the region, ZO-2, coding for a tight junction protein. Nine polymorphisms were detected and two of them were included in fine-mapping and association analysis. Fine-mapping defined the QTL result. To further verify the QTL, association analyses were carried out in two independent commercial breeding lines with the marker MCW241 and surrounding SNPs. Association was found mainly in a 0.8 Mb-wide chromosomal area on GGAZ.
  
  
  CONCLUSIONS
  There was good agreement between the location of the QTL region on chromosome Z and the association results in the commercial breeds analyzed. Variations found in tight junction protein ZO-2 and microRNA gga-mir-1556 may predispose egg layers to blood and meat spot defects. This paper describes the first results of detailed QTL analyses of the blood and meat spots trait(s) in chickens.
authors.affiliation: Biotechnology and Food Research, MTT, Jokioinen, 31600, Finland. mervi.honkatukia@mtt.fi
authors.forename: Mervi
authors.initials: M
authors.lastname: Honkatukia
authors.forename: Maria
authors.initials: M
authors.lastname: Tuiskula-Haavisto
authors.forename: Virpi
authors.initials: V
authors.lastname: Ahola
authors.forename: Pekka
authors.initials: P
authors.lastname: Uimari
authors.forename: Matthias
authors.initials: M
authors.lastname: Schmutz
authors.forename: Rudolf
authors.initials: R
authors.lastname: Preisinger
authors.forename: David
authors.initials: D
authors.lastname: Cavero
authors.forename: Pia
authors.initials: P
authors.lastname: Vennerström
authors.forename: Jesus
authors.initials: J
authors.lastname: Arango
authors.forename: Neil
authors.initials: N
authors.lastname: O'Sullivan
authors.forename: Janet
authors.initials: J
authors.lastname: Fulton
authors.forename: Johanna
authors.initials: J
authors.lastname: Vilkki
mesh_terms: D000818:Animals; D001483:Base Sequence; D001769:Blood; D002645:Chickens / Q000235:genetics*; D002874:Chromosome Mapping; D002875:Chromosomes / Q000235:genetics; D003433:Crosses, Genetic; D004531:Eggs / Q000592:standards*; D005260:Female; D008040:Genetic Linkage; D005838:Genotype; D008460:Meat; D035683:MicroRNAs / Q000235:genetics; D018895:Microsatellite Repeats; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide; D040641:Quantitative Trait Loci
chemical_list: D035683:MicroRNAs