Agarose gel electrophoresis of λ DNA sheared on two different days with varying geometries and flow rates. λ DNA (0.5 μg) was sheared under different conditions, separated by gel electrophoresis, and stained with ethidium bromide. The samples in lanes 1, 3,and 5 were sheared on one day, and those in lanes 2, 4, and 6 were sheared 3 days later. All samples were sheared by 20 passages through a length of small-bore tubing (0.0025 in.). (Lanes 1,2) The tubing was 6 mm long; (lanes3–6, the tubing was 3 mm long. The flow rate for samples in lanes 1–4 was 5.8 ml/min, and in lanes 5 and6, it was 8.7 ml/min. Five micrograms of a kilobase molecular mass marker was loaded in each of the outside lanes.