Power of a chromosomal test to detect genetic variation using genetic markers

The power of a backcross design to detect genetic variation associated with a single chromosome was investigated. A simple chromosomal test was suggested in which the phenotypic observations are regressed onto genotypic information from multiple markers. It was shown that the optimum marker spacing depends on the underlying genetic structure and chromosome length. A sparse marker map, with markers approximately every 50 cM, is sufficient to detect chromosomal variation if the nature of the genetic variance is coupled polygenes, whereas the optimum marker spacing to detect a single QTL somewhere on the chromosome is slightly denser, about 20–40 cM. Although the method was demonstrated for line crosses, it can equally be applied to other populations, for example four-way crosses and half-sib designs.