Efficiency of gene annotation of probes by ArrayGene. The height of the bars shows total number of probes in the array. No sequence id represents probes for which there was no sequence annotation available in the gene. Unknown position probes are those that the gene is known but it maps to multiple positions in the genome or to unordered scaffolds. Unspecific probes refer to those that can be associated with more than one Entrez Gene. Unknown sequence id refers to probes annotated with identifiers that could not be associated with an Entrez Gene. ArrayGene annotated probes are those that could be associated with a single Entrez Gene id that map to a known position in the genome. For the ABI platform, the No Sequence id fraction corresponds to about 4,000 probe targeting genes that have not been annotated by the public effort and are only available from the Celera gene discovery system.