Chromosome painting, or fluorescence in situ hybridization
| This technique was developed in the late 1980s
and is a powerful method to detect translocations (rearrangements
For the development of FISH, it was necessary to isolate each human
chromosome. Subsequently, DNA from these chromosomes was fragmented
and put into bacterial cells to amplify it (produce many copies).
In this way, a large number of copies of DNA from each chromosome
can be obtained.
These amplified DNA fragments are labeled with appropriate fluorescent
(light-emitting) dyes and allowed to hybridize (attach) to metaphase
chromosomes. The fluorescent-labeled DNAs will attach to the analogous
chromosomes from which they were derived. (DNA fragments with the
same base sequences have the characteristic of attaching to each
In this way, if a part of a painted chromosome (yellow, for example)
had undergone an exchange with another, non-painted chromosomes
(stained red), it is possible to detect the aberration (termed a
reciprocal translocation) because the aberrant chromosome contains
both yellow and red segments. Usually, a pair of bi-colored chromosomes
can be detected in one metaphase because two chromosomes typically
exchange a part of their DNA.
Reciprocal translocations are difficult to detect by simple staining
the entire set of chromosomes with a single material, such as with
Giemsa. Imagine, for example, a case with which the two exchanged
segments had similar lengths. The two translocated chromosomes should
appear perfectly normal, both in shape and length. If we employ
FISH, however, such translocation can be clearly detected.
Figure. An example of FISH-treated metaphase chromosomes
Here, chromosomes 1, 2, and 4 were
labeled yellow with FISH and the other chromosomes were
stained red. Translocations between yellow and red chromosomes
are detected. The left picture represents a normal cell
(the numbers in the figure indicate chromosome numbers)
and the right picture is an example of reciprocal translocation
with two bi-color chromosomes (indicated by two arrows).