title: Large scale analysis of positional effects of single-base mismatches on microarray gene expression data.
abstract: BACKGROUND
  Affymetrix GeneChips utilize 25-mer oligonucleotides probes linked to a silica surface to detect targets in solution. Mismatches due to single nucleotide polymorphisms (SNPs) can affect the hybridization between probes and targets. Previous research has indicated that binding between probes and targets strongly depends on the positions of these mismatches. However, there has been substantial variability in the effect of mismatch type across studies.
  
  
  METHODS
  By taking advantage of naturally occurring mismatches between rhesus macaque transcripts and human probes from the Affymetrix U133 Plus 2 GeneChip, we collected the largest 25-mer probes dataset with single-base mismatches at each of the 25 positions on the probe ever used in this type of analysis.
  
  
  RESULTS
  A mismatch at the center of a probe led to a greater loss in signal intensity than a mismatch at the ends of the probe, regardless of the mismatch type. There was a slight asymmetry between the ends of a probe: effects of mismatches at the 3' end of a probe were greater than those at the 5' end. A cross study comparison of the effect of mismatch types revealed that results were not in good agreement among different reports. However, if the mismatch types were consolidated to purine or pyrimidine mismatches, cross study conclusions could be generated.
  
  
  CONCLUSIONS
  The comprehensive assessment of the effects of single-base mismatches on microarrays provided in this report can be useful for improving future versions of microarray platform design and the corresponding data analysis algorithms.
authors.affiliation: Center for Statistical Sciences, Brown University, Providence, RI, USA. fduan@stat.brown.edu.
authors.forename: Fenghai
authors.initials: F
authors.lastname: Duan
authors.forename: Mark A
authors.initials: MA
authors.lastname: Pauley
authors.forename: Eliot R
authors.initials: ER
authors.lastname: Spindel
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: Robert B
authors.initials: RB
authors.lastname: Norgren