[BioC] Affymetrix probeset ids to gene symbols

[Maria Stalteri]

Hi Kurt, Jim,

Affymetrix arrays such as the hg-u133b were designed to target the 600 bp 
at the 3' end of the transcript, not the start of the transcript.

We have found that the many-to-one mappings between probesets and genes 
are often due to alternative splicing, use of alternative poly(A) sites, 
or annotation errors.

Cheers,
Maria