(a) Parental lines (P1 and P2) are crossed to produce an F1 generation. Common segregating generations used for QTL mapping are backcrosses of the F1 to either parental line (BC1, BC2), F2 derived from mating F1 individuals, and recombinant inbred lines (RILs) derived by inbreeding F2 families. (b-d) Experimental designs based on introgression. (b) Chromosome substitution lines, (c) introgression lines, (d) near-isogenic lines. Three chromosomes (C1 – C3) are depicted.