Illustration of a BSA experiment. a) Our model assumes a trait determined by a single QTL with two different alleles (A, a). The starting point of the experiment are two inbred parental strains, represented by red and blue chromosomes. The blue strain carries the A allele and the red carries the a allele. An F₁ population is created and interbred for t generations. At the end of the experiment, two pools of individuals are selected such that the first comprises only AA individuals and the second only aa individuals. The mapping resolution is determined by the length of the region surrounding the QTL for which all chromosomes in the AA-pool still have blue ancestry, while all in the aa-pool still have red ancestry. b) Mapping resolution in a simulated BSA experiment for a QTL located at the center (red line) of a 10-Mb-long chromosome (only showing the genomic segment between 3.5 and 6.5 Mb in figure). Interbreeding was modeled for 10 generations in a population of 100 individuals with a uniform recombination rate of 1.0 cM/Mb. Two pools of 10 AA and 10 aa individuals were selected at the end of the experiment. The blue curve shows the $G′$ statistic estimated from marker SNPs. The peak in $G′$ around the QTL indicates the region where all chromosomes in the AA/aa pools still have blue/red ancestry, which extends for $∼0.5$ Mb.