Fig. 3.

LOH analysis in intestinal tumors. (A) Het_Apc values for adenomas in B6 Min/+, AKR Min/+, and congenic B6 1638N/+ animals. Het_Apc was defined by the ratio of two ratios: the wild-type to mutant Apc band intensity ratio for tumor DNA normalized to that ratio for DNA from adjacent normal tissue prepared and analyzed completely in parallel to the tumor DNA. The values of Het_Apc for tumors in B6 Min/+ animals (orange bars) track with the previously published Gaussian distribution (white bars; mean 0.32 ± 0.17). The Het_Apc values for tumors in AKR Min/+ and B6 1638N/+ animals (cyan and purple bars, respectively) differ strongly from those of the B6 Min/+ LOH distribution. Instead, they lie in the range previously categorized as involving maintenance with silencing of the Apc⁺ allele (12). (B) Resolution of allele-specific PCR products. Allele-specific primer pairs were designed as described in Materials and Methods, giving PCR products for the 1638N mutant allele (249 bp) and the wild-type allele (225 bp) that were resolved on 6% polyacrylamide gels and quantitated with a PhosphorImager. Adenomas and adjacent normal tissue were dissected and frozen in liquid nitrogen. DNA was extracted, purified, and used as template for the production of dCTP-labeled PCR products. The measured Het_Apc values for tumors 1 and 2 were 0.84 and 0.77, respectively.