Click 'Filters' in the menu on the left hand side.
Expand 'Gene' panel.
Check the 'Input external references ID list' box to add the filter and add the list of gene IDs into the text box (or upload a file with the list of gene IDs). Also, be sure to select the correct format of gene IDs that you have used as the input from the drop-down list.
Click 'Attributes' in the menu on the left hand side.
Click the 'Sequences' radio-button option.
Expand 'Sequences' panel.
Check the 'Flank (Gene)' option.
Check the 'Upstream flank' box and input the desired length into the text box.
N.B You can also add important information into the sequence header by selecting different options from the options in the 'Header Information' panel.
Click 'Results' button in the top left--hand corner to view and download the results.