The key portion of the autoradiograph from a single locus probe analysis of various DNA samples in a rape investigation is shown in the figure.

If you are the DNA analyst, you should conclude that:

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Sometimes unrelated individuals will share alleles. In this case, the victim shares a band with Suspect B. To complicate things even further, the top band of Suspect A is very close to the band shared by B and the victim. The male fraction of the sexual assault evidence contains bands that are not found in Suspect A's profile. Therefore, A could not have contributed that DNA. In contrast, the male fraction of the evidence does not contain any bands that are not found in B's profile, so B cannot be excluded as a source of the evidentiary DNA.

The Biology Project
University of Arizona
April 7, 1997
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