A mammary gland EST showing linkage disequilibrium to a milk production QTL on bovine Chromosome 14

As part of a genome scan, ESTs derived fl om mammary gland tissue of a lact ating cow were used as candidate genes for quantitative trait loci (QTL). a ffecting milk production traits. Resource families were genotyped with 247 microsatellite markers and 4 polymorphic ESTs. It was shown by linkage anal ysis that one of these ESTs. KIEL_E8. mapped to the centromeric region of b ovine Chromosome (Chr-) 14. Regression analysis revealed the presence of a QTL. with significant effect on milk production. in this chromosome region. and analysis of variance showed no significant interaction of marker genot ype and family. The estimated significant differences between homozygous ma rl;er genotypes were 140 kg milk. -5.02 kg fat yield, and 2.58 he protein y ield for the first 100 days of lactation. Thus, there was strong evidence f or a complete or nearly complete linkage disequilibrium between KIEL_E8 and the QTL. To identify the biological function of KIEL_E8, we extended the s equence for 869 bp by 5 ' -RACE. A 560-bp fragment of this shows a 90.9% si milarity to a gene en coding a cysteine- and histidine-rich cytoplasmic pro tein ill mouse. Although such a protein may have a regulatory function for lactation and a linkage disequilibrium between the EST marker and the QTL h as been observed, it remains to be elucidated whether they are identical or not. Nevertheless. KIEL_E8 will be an efficient marker to perform marker-a ssisted election in the Holstrin-Friesian population.