A QTL AFFECTING MILK-YIELD AND COMPOSITION MAPS TO BOVINE CHROMOSOME-20 - A CONFIRMATION

As part of a whole genome scan undertaken to detect quantitative trait loci (QTL) affecting milk yield and composition, we have genotyped a granddaughter design comprising 1152 sons for six microsatellite marke rs spanning bovine chromosome 20. An analysis performed across familie s provided strong evidence (experiment-wise P-values < 0.01) for the p resence of a QTL affecting primarily protein percentage towards the te lomeric end of the chromosome. A founder sire, shown in a previous stu dy to segregate for a similar QTL in the corresponding chromosome regi on, was characterized by 29 and 57 sons and maternal grandsons, respec tively, in the present design. Sorting corresponding sons and grandson s by paternal or grandpaternal allele provided significant evidence fo r the segregation of a QTL on chromosome 20. Altogether these results confirm the location of a QTL affecting milk production on bovine chro mosome 20.