Multistage QTL mapping strategy in an advanced backcross cattle population

The aim of this study was to identify quantitative trait loci (QTL)
affecting milk production traits in one advanced backcross
Fleckvieh x Red Holstein population, that are identical by descent,
according to both origin and effect.Genome wide scan and consequent
QTL mapping by means of “selective DNA pooling” in the daughter
design revealed two advanced backcross (Fleckvieh x Red Holstein)
families segregating for QTL affecting protein percent (PP-QTL) on
bovine chromosome 19 (BTA19). Identical by descent analysis
indicated a 20 cM region as the most possible location of this QTL.
After initial interval mapping in 20 granddaughter design families,
six families segregating for PP-QTL in the same region were
detected. PP-QTL segregating and related families were combined
into a set of 11 granddaughter design families for intensive study
performed with 21 microsatellite markers. Final interval mapping
was able to confirm but not to refine the PP-QTL position. Combined
linkage disequilibrium and linkage mapping refined the PP-QTL
position. By this method we were able to locate highly significant
PP-QTL in the region of 4-9 cM. Analyses performed on all available
traits showed effects of the mapped QTL on milkability also. The
analysis of estimated sires’ effects suggests rather one QTL with
effect on both traits.