I'm working with gene expression data, and one thing that I notice is that some of the genes are repeated. For example, GSE12051 has the gene "ABL1" twice.
Why is this? If I wanted to know the gene expression of "ABL1" should I be taking the arithmetic mean of the two measurements?
This is a microarray data. In microarray, a gene can be represented by more than one probe/probeset. As a result, you see different expression values corresponding to different probes. You will have to be careful as different probes can represent different transcripts/isoforms or same transcripts.