Dear BioC, I'm trying to learn about Affymetrix Tiling Arrays and I have a few questions regarding the array design of the Yeast Tiling array (Sc03b_MF_v04.bpmap). 1. One of the sequences is labeled as "chloroplast" what is this sequence and what is its purpose? 2. Some chromosomes are listed under 2 sequence sets and the PM Position numbers do not match up - there are gaps in the sequence. Why? 3. What is the purpose of the gcBinXX sequences? Are they control sequences? How are they organized? 4. What are the r2_ and X_ sequences? Any kind of help would be appreciated. Sincerely, -Igor