Chromosome For the SAM, BAM, and Eland Input Engine Processes: For the Gene Model Summary Process: For the SAM, BAM, and Eland Input Engine Processes: Specify a variable indicating the chromosome . To Specify the Chromosome Variable: Specify an Annotation File . The Available Variables field is automatically populated with variables from the specified file. Left-click a variable from the Available Variables field. Click to add the selected variable to the Chromosome field.