Distribution of N2 progeny from the B6 and D2 backcrosses to D2B6F1Apc^Min /+ mice based on polyp number in the small intestine and genotypes at the Mom1 and Mom2 loci. N2 offspring (Table 1) were genotyped for the Pla2g2a gene (see Methods) to determine whether they carried the B6 susceptibleMom1^S allele and/or the D2 resistantMom1^R allele. N2 offspring were phenotyped for polyp number to determine whether they were homozygous for susceptibleMom2 (Mom2 ⁺/Mom2 ⁺) alleles (≥25 polyps = high-polyp phenotype) or whether they were heterozygous for the resistant Mom2^R (Mom2^R /Mom2 ⁺) allele (≤24 polyps = low-polyp phenotype); molecular markers on mouse chromosome 18 were consistent with the determination of Mom2 allele status (Fig. 2). Genotypes at the Mom1 and Mom2 loci are shown to the right. (A) A total 79 N2 offspring were generated from the backcross to B6, and (B) a total of 21 N2 offspring were generated from the backcross to D2 (Table 1).