For this presentation, a genetic aberration is defined as an abnormality of the chromosome number in a cell. Below are some genetic aberrations that can be detected by FISH.
Amplifications involve the gain of a segment of a chromosome, usually a gene.
Deletions involve the loss of a segment of a chromosome. Terminal deletions involve the end of a chromosome. The result is one piece of the chromosome that contains the centromere. The other piece of the chromosome that does not contain a centromere is called an acentric fragment. The acentric fragment is lost during the next division because it cannot attach to the spindle fibers to migrate to the daughter cells. An interstitial deletion involves two breakpoints within one arm. The DNA material between the two breakpoints is lost.
A translocation occurs when a segment of DNA moves from the original chromosomal location to a different location on another chromosome, as shown in the image on the right. The breakpoint is the area where the chromosome breaks and it may involve a whole gene or a portion of a gene or multiple genes. Some translocations do not interfere with gene function, but oftentimes, translocations cause the gene to malfunction and produce a chimeric protein with another gene. Translocations will have a profound effect on the cell during mitosis. Chromosomes pair up in a very specific way during mitosis and translocations can wreak havoc with this process causing chromosomes not to separate appropriately and leading to increased aneuploidy.