In Situ Hybridization

Described in more detail in Chapter 18, in situ hybridization is another method for determining the chromosomal location of a particular gene. This method requires a DNA copy of the gene or its RNA product, which is used to make a molecule (called a probe) that is complementary to the gene of interest. The probe is made radioactive or is attached to a special molecule that fluoresces under ultraviolet (UV) light and is added to chromosomes from specially treated cells that have been spread on a microscope slide. The probe binds to the complementary DNA sequence of the gene on the chromosome. The presence of radioactivity or fluorescence from the bound probe reveals the location of the gene on a particular chromosome (FIGURE 7.22a). The use of fluorescence in situ hybridiza

7.22 In situ hybridization is another technique for determining the chromosomal location of a gene. (a) FISH technique: in this case, the bound probe reveals sequences associated with the centromere. (b) SKY technique: 24 different probes, each specific for a different human chromosome and producing a different color, identify the different human chromosomes. (Courtesy of Dr. Hesed Padilla-Nash and Dr. Thomas Ried, NIH.)

tion (FISH) has been widely used to identify the chromosomal location of human genes. In spectral karyotyping (SKY) (< Figure 7.22b), a set of 24 FISH probes, each specific to a different human chromosome and attached to a molecule that fluoresces a different color, allows each chromosome in a karyotype to be identified. More on fluorescence in situ hybridization (FISH)

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