QUANTITATIVE TRAIT LOCUS MAPPING USING SETS OF NEAR-ISOGENIC LINES - RELATIVE POWER COMPARISONS AND TECHNICAL CONSIDERATIONS

The power to detect QTL using near-isogenic line (NIL) comparisons ver sus recombinant inbred (RI) populations was assessed. The power to det ect QTL was found to be generally greater when using RI populations th an when using NIL contrasts. Power to detect QTL with NIL contrasts ne ver exceeded that of RI populations when the number of RI lines is max imized relative to replication of lines for a given number of experime ntal units. The relative power of NIL contrasts is highest for traits with high heritability and when a gain in precision is realized due to increased replication of entries. Although NIL populations are genera lly less powerful than RI populations of similar size, some practical considerations may enhance the value of these materials. Availability of NILs allows the genetic effect of a specific chromosome region to b e determined by comparing two lines; all RI lines in a population need to be rescored for each new trait even if the effect of a specific ch romosome region is suspected. NIL comparisons may allow genetic differ ences to be detected by visual inspection; genetic effects can only be expressed as means and variances with recombinant inbred populations. In summary, RI populations generally, and in some cases, substantiall y, provide better power for QTL detection than NIL comparisons. Practi cal considerations, however, indicate that many factors need to be con sidered when choosing a population structure to meet an experimental o bjective.