Good day,
I can't reproduce the problem on Windows, so it seems specific to MacOS.
Is having 5' and 3' labels at the same ends of both DNA strands biologically incorrect? DNA strands are anti-parallel. See http://www.phschool.com/science/biology_place/biocoach/dnarep/strands.html Perhaps making the line corresponding to the strand the gene is encoded on thicker than the other line might also be useful?
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Dario Strbenac
University of Sydney
Camperdown NSW 2050
Australia