DNase I cuts DNA that is not protected by bound proteins but is unable to cut DNA that is complexed with proteins. Human DNA is isolated, stripped of its nonhistone proteins, and mixed with DNase I. Samples are removed after 30 minutes, 1 hour, and 4 hours and run separately in gel electrophoresis. The resulting gel is stained to make all DNA fragments in it visible, and the results are shown in the figure. DNA fragment sizes in base pairs (bp) are estimated by the scale to the left of the gel. Examine the gel results and speculate why longer DNase I treatment produces different results.