Definition: In a translocation, a segment of one chromosome is transferred to another.

Types

 constitutional translocation
 tumoral translocation

Balanced reciprocal translocation

In balanced reciprocal translocation, there are single breaks in each of two chromosomes, with exchange of material. Such a translocation might not be disclosed without banding techniques. Because there has been no loss of genetic material, the individual is likely to be phenotypically normal.

A balanced translocation carrier is at increased risk for producing abnormal gametes. Such a gamete would be unbalanced because it would not contain the normal complement of genetic material. Subsequent fertilization by a normal gamete would lead to the formation of an abnormal (unbalanced) zygote, resulting in spontaneous abortion or birth of a malformed child.

Robertsonian translocation

The other important pattern of translocation is called a robertsonian translocation (or centric fusion), a translocation between two acrocentric chromosomes. Typically the breaks occur close to the centromeres of each chromosome. Transfer of the segments then leads to one very large chromosome and one extremely small one.

Usually the small product is lost; however, because it carries only highly redundant genes (e.g., ribosomal RNA genes), this loss is compatible with a normal phenotype. Robertsonian translocation between two chromosomes is encountered in 1 in 1000 apparently normal individuals.

See also

 oncogenic chromosomal translocation

References

 Rabbitts TH, Stocks MR. Chromosomal translocation products engender new intracellular therapeutic technologies. Nat Med. 2003 Apr;9(4):383-6. PMID: #12669051#

 Aplan PD. Causes of oncogenic chromosomal translocation. Trends Genet. 2006 Jan;22(1):46-55. PMID: #16257470#

 Greaves MF, Wiemels J. Origins of chromosome translocations in childhood leukaemia. Nat Rev Cancer. 2003 Sep;3(9):639-49. PMID: #12951583#

 Rego EM, Pandolfi PP. Reciprocal products of chromosomal translocations in human cancer pathogenesis: key players or innocent bystanders? Trends Mol Med. 2002 Aug;8(8):396-405. PMID: #12127726#

 Tomescu O, Barr FG. Chromosomal translocations in sarcomas: prospects for therapy. Trends Mol Med. 2001 Dec;7(12):554-9. PMID: #11733218#