Rice Genetics IV - IRRI books - International Rice Research Institute

In summary, in QTL analysis of a population in which a QTL with a large effectwill segregate, a putative gene effect of an epistatic QTL can be recognized as a smalleffect only, even if the actual gene effect is large. The complex inheritance of quantitativetraits is probably explained mainly by multigenic control, but epistatic interactionis also an important factor in such complexity.Molecular dissection of a complex traitMap-based cloning or candidate identification of genes at QTLsFigure 4 shows a procedure for the molecular identification of genes at QTLs fromdetection to cloning. After the detection of putative QTLs with major effects in aprimary mapping population, the construction of special genetic stocks, such as NILsor substitution lines, can be effectively and efficiently achieved by using MAS. Forsome traits that can be evaluated with high reliability, such as heading date and culmlength, high-resolution and fine-scale mapping of putative QTLs as Mendelian factorswill be feasible by combining the use of NILs and ordinal linkage mapping basedon progeny testing. For traits whose expression and performance are affected largelyby environmental factors, it would be more difficult to employ simple progeny testing,such as F 2 plant/F 3 lines. In such a case, advanced progeny testing might beLine A × Line BF 2BC 1 F 1F 1 × Line AQTL analysisAdvanced backcross progenyNILs for target QTLsBC n F nCharacterization of QTLsMapping of target QTLs asa single Mendelian factorLarge segregatingpopulation for target QTLMarker-assistedselectionHigh-resolution mapping of target QTL based on ordinalprogeny or advanced progeny testingsSequencing of candidate region, gene prediction,expression profiling, and genetic complementation ofcandidate geneMolecular cloning of genes at QTLsFig. 4. Schematic representation of a strategy for map-based cloningof genes at QTLs. NILs = near-isogenic lines.Naturally occurring allelic variations as a new resource . . . 233