POWER ANALYSIS FOR QUANTITATIVE TRAIT LOCUS MAPPING IN POPULATIONS DERIVED BY MULTIPLE BACKCROSSES

Populations derived by multiple backcrosses are potentially useful for quantitative trait locus (QTL) mapping studies. Comparisons of relati ve power to detect QTL using populations derived by multiple backcross es are needed to make decisions when mapping projects are initiated. T he objective of this study was to theoretically compare the power to d etect QTL in populations derived by multiple backcrosses relative to m apping in a recombinant inbred population of equal size. Backcrossing results in a reduction in genetic variance with each generation and al so results in an increasing frequency of the recurrent parent marker g enotype. The relevant outcome for QTL mapping is a reduction in geneti c variance to partition between marker genotype classes and increasing unbalance of the number of individuals contributing to the mean of th e marker genotypes. Both of these factors lead to a decrease in the po wer to detect a QTL as the number of backcross generations increases. Experimental error was held constant with the populations compared. Fr om a theoretical standpoint, backcross-derived populations offer few a dvantages for QTL detection. If, however, a backcrossing approach is t he most efficient method to achieve a desired breeding objective and i f QTL detection is an objective of equal or less importance, backcross -derived populations are a reasonable approach to QTL detection.