MAPPING QUANTITATIVE TRAIT LOCI WITH DNA MICROSATELLITES IN A COMMERCIAL DAIRY-CATTLE POPULATION

Individual loci affecting economically important traits can be located using genetic linkage between quantitative trait loci and genetic mar kers. In the 'granddaughter' experimental design, heterozygous grandsi res and their sons are genotyped for the genetic marker, while the qua ntitative trait records of the granddaughters are used for statistical analysis. Ten DNA microsatellite markers were used to look for associ ations with quantitative trait loci affecting milk production traits i n seven Israeli Holstein grandsire families. At least 60% more grandsi res were heterozygous, and 40% fewer individuals were discarded becaus e of unknown paternal allele origin, as compared with diallelic marker s. The effects of paternal alleles for locus D21S4 on kg milk and prot ein were significant (P < 0.025). The allele substitution effects for sire 783 were 283 kg milk and 5.7 kg protein. For both traits progeny of sire 783 that inherited allele '18' had higher evaluations than pro geny that inherited allele '21'. These results were verified by genoty ping 151 of his daughters. Thus, the rate of genetic gain for protein production can be increased by selecting progeny of sire 783 carrying allele '18' at this locus.