Thinking Like a Biotechnician
1. Give plausible reasons for the following results on your gel.
a. When stained and visualized on the UV light box, other gels have many bands and smears of
DNA. Your gel has no bands, smears, or anything on it. What may have caused these results?
b. A sample that is supposed to give a straight, single band of high molecular weight, instead
has a big smear of DNA down most of the lane. What may have caused this smearing?
c. All the bands and smears of samples are located right next to the wells and have not
moved very far. What may have caused this?
2. On semi-log graph paper, plot the distance the DNA standard fragments traveled from the
wells (in mm) on the horizontal axis versus their size (in base pairs) on the vertical axis.
Draw a “best-fit” straight line that represents how DNA fragments of different lengths move
through the gel. Use this graph to estimate the sizes of the plasmid bands.
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Chapter 4 Laboratory Manual