ANOVA among groups classified by combined genotyping. (NZW x B10.NZW) F1 x B10.NZW backcross mice were subdivided into four groups (A to D) according to combined genotyping of loci,D13MIT136 (Bpal-2) and D17MIT222. Symbol ‘+’, genotyped as NB (heterozygous for NZW and B10.NZW) and ‘−’, genotyped as BB (homozygous for B10.NZW). P values of post hoc test (Fisher’s Protected Least Significant Difference test) were as follows: at 8 months old; A versus C, P < .05; A versus D, P < .0001; B versus D, P < .0001; C versus D, P < .005; at 16 months old; A versus D, P< .0005; B versus D, P < .005; C versus D, P < .05.