Principles of Fluorescence Spectroscopy

728 DNA TECHNOLOGY
Figure 21.48. Schematic of a DNA hybridization array using QD-labeled microbeads. From [148].
Figure 21.49. Emission spectra of a single type of microbead after
equilibration with its target sequence. The target oligomer was labeled
with Cascade Blue emitting near 440 nm using biotin-streptavidin
chemistry. From [148].
more chromosomes. The probe DNA is labeled with one or
more fluorophores. Following exposure to the probe DNA,
one or more of the chromosomes become fluorescent.
Alternatively, the probe DNA can be specific for the centromeric
or telomeric region of chromosomes, in which
case only the ends of the chromosomes become fluorescent.
DNA probes can also be specific for small regions of DNA
representing one or several genes. FISH can also be used
with dispersed DNA in interphase cells, typically to detect
individual genes. When first introduced in-situ hybridization
was performed using radioactive traces and radiography.
At present in-situ hybridization is performed almost
exclusively using fluorescence.
21.7.1. Preparation of FISH Probe DNA
Preparation of probe DNA to identify individual genes is
relatively straightforward. A DNA oligomer with the gene
sequence and appropriate primer sequences is synthesized.
This task was aided by completion of the human genome in
Figure 21.50. Schematic of fluorescence in-situ hybridization (FISH).