Howdunit Forensics by D P Lyle

Author:D P Lyle
Language: eng
Format: epub
Tags: ebook, book
Publisher: F+W Media
Published: 2011-04-09T16:00:00+00:00

Figure 10-2: The DNA fingerprint. Electrophoresis separates DNA sample fragments according to size, which results in columns of bands that can be compared with other samples.

The autorad gives you a picture of the DNA fragment pattern at a particular locus. This alone will not give you conclusive match, since some people share similar patterns at a single locus. It may, however, exclude a suspect. When comparing a known and an unknown DNA sample, if any band in the RFLP autorad doesn’t match, the two samples in question did not come from the same person. To make a match, multiple loci must be examined. We’ll look more deeply into why multiple loci are needed later.

PATTERN MATCHING

When the forensic lab must match one or more samples, the electrophoretic gel is divided into several parallel columns called lanes. A DNA sample is placed at the beginning of each lane. When the electrophoresis process begins, the fragments in each lane move and separate independent of each other. This causes each sample to separate into a series of bands determined by the size of the various fragments in each sample. A match is made when the bands in the known and unknown columns match. This comparison can be done visually or with the aid of a computer.

The samples placed at the head of each column vary. Some may be control materials, such as DNA from bacteria, viruses, or lab-synthesized DNA. These are DNA samples with fragments of known size and can be used to estimate the size of fragments in any unknown samples. More importantly, one column contains the crime scene specimen and other columns contain samples from any suspects.

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