Chromosome 13 loss of heterozygosity (LOH) and copy number aberrations in spontaneous and radiation-induced medulloblastomas from Ptch1^+/– mice. Chromosomal regions and positions of polymorphic markers are shown on the left and right side of the schematic chromosome, respectively. Open circles indicate loss of a C3H allele, and filled circles indicate retention of both B6 and C3H alleles. Note that the wild-type Ptch1 allele is located on the C3H chromosome in these mice. Large circles indicate the results of LOH obtained from polymorphic markers, and small circles indicate the results of LOH obtained from a single-nucleotide polymorphism (SNP) in exon 23 of Ptch1. Panel A: LOH patterns of S-type and R-type tumors. S-type tumors are marked by allelic losses at all consecutive markers distal to the Ptch1 locus, indicated with gray shading, whereas R-type tumors show allelic loss(es) only at markers in the interstitial region around or within the Ptch1 locus; N-type tumors were without LOH. Panel B, left side: LOH patterns of tumors with multiple deletions having a hemi-allelic loss at interstitial sites involving the Ptch1 locus and another allelic loss at distal sites. LOH of these types existed only in neutron-induced MBs [0.5 Gy at P4 (sample no. 1), 0.1 Gy at P10 (no. 2 and 4), and 0.5 Gy at P10 (no. 3)]. Panel B, right side: Results of the DNA copy number analysis, indicating the consistency of these LOH patterns.