Chromosomal imbalances in papillomas detected by SSLP analysis. (a) SSLP analysis results for a representative microsatellite marker of normal genomic DNA (N) and of DNA from two independent papillomas (P1 and P2) from three different N4 mice (A, B and C). The upper band represents the NIH/Ola allele, whereas the lower band represents the M. spretus allele. Three papillomas show preferential imbalance in favor of the NIH/Ola allele (P1 from mice A, B and C), one shows preferential imbalance in favor of the M. spretus allele (P2 from mouse A), and two papillomas do not show detectable imbalance at this marker (P2 from mice B and C). (b) Summary of chromosomal imbalances detected by SSLP analysis in papillomas from N2 (n=27), N4 (n=49) and N9 mice (n=50). The mean percentages of imbalances and s.e. are shown for at least three markers on proximal chromosome 7. The closed part of each bar represents NIH/Ola allele amplification or M. spretus allele loss, whereas the open part of each bar represents M. spretus allele amplification or NIH/Ola allele loss. (c) Detailed analysis of imbalance patterns on chromosome 7 in papillomas. Open circles represent no imbalance; closed circles represent imbalance in favour of the NIH/Ola allele. Most papillomas showed gain of the whole region (34 papillomas) but others showed region-specific gains that facilitated identification of the most commonly amplified markers. (d) Frequency of somatic genetic changes detected by SSLP analysis within the region from 20.9 to 21.8 cM on chromosome 7. Data were derived from papillomas (n=78) from N9 mice or from different congenic lines showing significant linkage with papilloma incidence at Skts1 (i.e. lines 3540, A62, 717 and C3F). Indicated are the percentages of imbalances for different markers. The physical location of the markers in Mb is based on data from the Ensembl database (Version 40) (http://www.ensembl.org).