Multiple quantitative trait locus analysis of bovine chromosome 6 in the Israeli Holstein population by a daughter design

Nine Israeli Holstein sire families with 2978 daughters were analyzed for q uantitative trait loci effects on chromosome 6 for five milk production tra its by a daughter design. All animals were genotyped for 2 markers. The thr ee families with significant effects were genotyped for up to 10 additional markers spanning positions 0-122 cM of BTA6. Two sires were segregating fo r a locus affecting protein and fat percentage near position 55 cM with an estimated substitution effect of 0.18% protein, which is equivalent to one phenotypic standard deviation. This locus was localized to a confidence int erval of 4 cM. One of these sires was also heterozygous fora locus affectin g milk, fat, and protein production near the centromere. The hypothesis of two segregating loci was verified by multiple regression analysis. A third sire was heterozygous for a locus affecting milk and protein percentage nea r the telomeric end of the chromosome. Possible candidates for the major qu antitative gene near position 55 cM were determined by comparative mapping. IBSP and SSP1 were used as anchors for the orthologous region on human chr omosome 4. Twelve genes were detected within a 2-Mbp sequence. None of thes e genes have been previously associated with lactogenesis.