Investigating CSI – Background material Table of Contents I ...

For example, in the first loci (which spans the region from 100-150 base pairs)
the victim could have 15 sequence repeats from her mother and 16 from her
father, while, the suspect could have 20 repeats from his mother and 18 from his
father. The PCR reaction with the fluorescein-labeled primers would have
attached tags onto each length of repeats. When the sample is run through
electrophoresis, the fluorescein tag would be illuminated, and a reading would be
taken. As we know, smaller samples run faster through electrophoresis, thus the
lane containing the victim’s DNA (which contains some 15-repeat segments and
some 16-repeat segments) would fluoresce and give a reading before the lane
containing the suspect’s DNA (containing 18- and 20-repeat segments).
The victim’s results would show two peaks for the first loci, one at 15 and one at
16. The suspect’s results would also show two peaks for the first loci, but they
would be at 18 and 20. Each of the five loci shown above would contain two
peaks for both the victim’s results and the suspect’s results.
………………………………………………………………….
100 120 140 160
15
16
…………………………………………………………………..
100 120 140 160
18
52
20
Victim’s results
Suspect’s
results