Table 2

Probability of observed fixations due to chance

The probability of the observed number of fixations of lesions in loci based on the exact binomial probability with pb = 0.011. A fixation is defined as a lesion that is observed in greater than 90% of the sampled proliferating cells in a Barrett’s segment. These data suggest that lesions in p16 and p53 go to fixation more frequently than would be expected if they were neutral mutations being fixed as hitchhikers. Note that fixations of the LOH events that inactivate p53 may be distributed among any of the microsatellites linked to p53 and so some linked loci show more significant signs of selection than other loci. In addition, LOH in some microsatellites near p53 such as TP53Di are probably not detected as selected loci because they are frequently uninformative and are particularly sensitive to low levels of normal cell contamination, which obscures LOH in these loci.

Fixation of lesionBinomial probability that fixations are hitchhikers
p16 methylation<0.001
p16 mutation<0.001
9p (p16) LOHa (D9S2169, D9S935, D9S925, D9S932, D9S1121, D9S1118)<0.001
p53 mutation<0.001
17p (p53) LOH
 TP53, D17S1303, D17S1298<0.001
 D17S1537, D17S974<0.01
9q LOH
17q LOH (D17S1294, D17S1293, D17S1290, D17S1301) and TP53Di≥0.05
Aneuploidy and tetraploidy≥0.05
All microsatellite shifts≥0.05
  • a LOH, loss of heterozygosity.