APPLICATION OF A CANONICAL TRANSFORMATION TO DETECTION OF QUANTITATIVE TRAIT LOCI WITH THE AID OF GENETIC-MARKERS IN A MULTI-TRAIT EXPERIMENT

Effects of individual quantitative trait loci (QTLs) can be isolated w ith the aid of linked genetic markers. Most studies have analyzed each marker or pair of linked markers separately for each trait included i n the analysis, Thus, the number of contrasts tested can be quite larg e. The experimentwise type-I error can be readily derived from the nom inal type-I error if all contrasts are statistically independent, but different traits are generally correlated. A new set of uncorrelated t raits can be derived by application of a canonical transformation, The total number of effective traits will generally be less than the orig inal set. An example is presented for DNA microsatellite D21S4, which is used as a marker for milk production traits of Israeli dairy cattle . This locus had significant effects on milk and protein production bu t not on fat. It had a significant effect on only one of the canonical variables that was highly correlated with both milk and protein, and this variable explained 82% of the total variance. Thus, it can be con cluded that a single QTL is affecting both trails. The effects on the original traits could be derived by a reverse transformation of the ef fects on the canonical variable.