Course: SAT 170 Introductory Biotechnology

Unit 7 Learning Module

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Page 2 of 5
DNA Technology Part 2 (continued)

Figure 1
Fluorescence In Situ Hybridization (FISH) is a technique that is commonly used to detect the location of a particular DNA sequence within a larger piece of DNA such as a chromosome. During the FISH process, the chromosomes are isolated from the cells of a particular organism. These chromosomes are then applied to a glass microscope slide. A probe which is complementary to the gene of interest is then added to the slide. If the probe is able to locate its complementary sequence in any of the chromosomes, it will bind to that DNA sequence. The slide can then be washed to remove any unbound probe and then examined under fluorescent light. The probe will be illuminated upon exposure to the fluorescent light, and can thus be used as an indicator of the presence and chromosomal location of a DNA sequence of interest. FISH can be useful for studying an organisms complete set of chromosomes as well as detecting genes that have been associated with particular disorders.

Figure 1: The result of the FISH technique is to see the labeled probe(s) at specific locations in the chromosome, which confirms the presence and location of their complementary DNA sequences (see the red and green fluorescent regions of the chromosomes here).

In a process similar to the Western and Eastern blots discussed in unit 5, chromosomes can be evaluated for the presence of particular gene or sequence of DNA. This technique, known as the Southern Blot was actually the first of its kind and the basis for the aforementioned techniques. During the southern blot analysis, the chromosomes are digested with restriction enzymes once they have been isolated from the cells of a particular organism. The resulting chromosome fragments are then separated using electrophoresis. Once electrophoresis is complete, the fragments are transferred to a nitrocellulose membrane, using a technique known as blotting. This technique involves sandwiching the gel with the nitrocellulose membrane as was described with the Eastern and Western blotting technique. The blot can then be incubated with a labeled probe that is complementary to the gene of sequence that you are trying to detect. Much like the FISH technique, the detection of this label is an indicator of the presence of that gene or DNA sequence.

Figure 2: In this image you can see researchers transferring an electrophoresis gel to nitrocellulose paper for the Southern Blot technique.
Figure 2