MAPPING OF SERUM AMYLASE-1 AND QUANTITATIVE TRAIT LOCI FOR MILK-PRODUCTION TRAITS TO CATTLE CHROMOSOME-4

The present study was undertaken to confirm and refine the mapping of a quantitative trait locus in cattle for milk fat percentage that had earlier been reported to be linked to the serum amylase-1 locus, AM1. Five half-sib families from the previous study and 7 new ones were gen otyped for nine microsatellite markers spanning chromosome 4. AM1 was mapped between the microsatellite markers BMS648 and BR6303. In a gran ddaughter design, interval mapping based on multiple-marker regression was utilized for an analysis of five milk production traits: milk yie ld, fat percentage and yield, and protein percentage and yield. In the families reported on previously, significant effects for fat and prot ein percentages were detected. In the new families, an effect on milk and fat yields was found. The most likely positions of the quantitativ e trait locus in both groups of families were in the same area of chro mosome 4 in the vicinity of the obese locus. Direct effects of the obe se locus were tested for using polymorphism in two closely linked micr osatellites located 2.5 and 3.6 top downstream of the coding sequence. No firm evidence was found for an association between the obese locus and the tested traits.