To improve genetic resolution, an N2F1 backcross mapping strategy between the GC tumor–susceptible SWXJ-9 RI strain and the evolutionarily divergent Mus musculus castaneus (CAST) strain confirmed Gct1 as the fundamental locus for tumor initiation contributed by SWR and identified three novel autosomal loci, Gct7 on Chr 1, Gct8 on Chr 2, and Gct9 on Chr 13, and two epistatic interactions between loci on Chrs 17 and 18 and between loci on Chrs 2 and 10 (Dorward et al. 2005). Here, INTS13 is linked to neoplasm.