Once a mapping population has been created, the next step in the genetic mapping process is
to genotype individual F2 progeny using genetic markers distributed throughout the genome.
For our mapping experiments we made use of insertion/deletion (INDEL) polymorphisms
between the Col and Ler ecotypes that had been previously characterized (Salathia et al.,
2007). The 22 INDEL markers that we chose are spaced across all five chromosomes so that
a given gene is no more than ca. 20 centiMorgans from the nearest marker (Figure 2b and
Table S1). We designed PCR primers for each marker that are able to amplify products from
both Landsberg and Columbia templates (Figure 2c). Differences in the sizes of the PCR
products amplified from the two ecotypes allow one to determine if plants are homozygous
Col, homozygous Ler, or heterozygous at each of the marker loci (Figure 2d).