Hi friends: I find that there are multiple instances of probes (i.e., the same 25-mer sequence) on the same array. For example: -------------- > library("hgu133atagprobe") > seqnc <- hgu133atagprobe$sequence ------------- There are 248152 probes, out of which 6067 are duplicated (the number varies between 2 and 20). ------------- > length(seqnc) [1] 248152 > sum(duplicated(seqnc)) [1] 6067 > numTimes = sapply(unique(seqnc[duplicated(seqnc)]), function(x) sum(seqnc==x)) > range(numTimes) [1] 2 20 ------------- I have the question in mind: what is the logic behind multiple instances of the same probes (e.g., quality control?) I thank in advance for any feedback or pointer to literature. Saroj