<p>I am currently using some genes in Affymetrix format, like:
- 200007<em>at 
- 200011</em>s<em>at 
- 200012</em>x_at</p>

<p>What do "<em>at", "</em>s<em>at", and "</em>x_at" stand for?</p>

<p>Thanx</p>

<p><a href="http://www.affymetrix.com/support/help/faqs/mouse_430/faq_8.jsp">Here</a> is an answer from the Affymetrix FAQ:</p>
<p>The last three characters identify the probe set strand. Probe sets that are designed to detect the anti-sense strand of the gene of interest are annotated with "_at". Probes in an identical probe set (_s set) all cross-hybridize to the same set of sequences that are used for the design (including any additional pruning sequences if provided). Probes in a mixed probe set (_x set) contain at least one probe that cross-hybridizes with other sequence(s) used for the design.</p>
<p>See tjhe above link for more information, including a nice figure depicting these relationships and definitions.</p>