Historical overview of detecting deletions molecular cytogenetic

The term "deletion" describes a structural chromosome aberration in which a part of a chromosome arm or an extensive region of DNA is missing from its normal location. Thus, deletion is the practical loss of chromosomal material and any genes that map to the region of the genome that is missing. The simplest type of deletion encountered clinically is an interstitial deletion (see Figure 1), and small deletions are referred to as microdeletions. With standard FISH methods, BACs mapping to the missing region are labeled with colored fluorochromes and the presence or absence of the FISH signal determines if a deletion is present or not. There are many examples of inherited deletions and microdeletion syndromes in the genetic literature Two color FISH analysis of metaphase cells is commonly used to detect presence or absence of a region of interest such as a microdeletion.

Figure 1 Schematic depiction of large interstitial deletion of part of a chromosome arm. In this example several cytobands (shown in blue) are lost after the deletion has taken place.