I was wondering what uncoloured rectangles signify in the image plots. Thanks Krys Dr Krystyna A Kelly (Krys) Department of Pathology University of Cambridge, Tennis Court Road, Cambridge CB2 1QP Tel: 01223 333331 and MRC Biostatistics Unit Institute of Public Health, Robinson Way, Cambridge CB2 0SR Tel: 01223 767408 Email: kak28 at cam.ac.uk