Effect of colony size on amplitude of erythroid output. The difference in amplitude of erythroid output between DBA and normal cells in liquid culture is caused primarily by a difference in colony size. Photomicrographs of representative colonies from normal and DBA cultures at limiting (0.2 U/mL) and standard (2 U/mL) concentrations of Epo show difference in colony size. Colonies were visualized using an Olympus CK40 inverted microscope equipped with an Olympus Camedia 3030 camera and a 10 ×/10 objective lens (Olympus, Southall, Middlesex, United Kingdom). Images were processed with Microsoft Photo Editor (Microsoft, Reading, United Kingdom).