Chromosomal translocation

Translocations can be balanced (in an even exchange of material with no genetic information extra or missing, and ideally full functionality) or unbalanced (where the exchange of chromosome material is unequal resulting in extra or missing genes).

[1][2] Reciprocal translocations are usually an exchange of material between non-homologous chromosomes and occur in about 1 in 491 live births.

[3] Such translocations are usually harmless, as they do not result in a gain or loss of genetic material, though they may be detected in prenatal diagnosis.

For example, carriers of Robertsonian translocations involving chromosome 21 have a higher risk of having a child with Down syndrome.

Robertsonian translocations involving chromosome 14 also carry a slight risk of uniparental disomy 14 due to trisomy rescue.

The initiating event in the formation of a translocation is generally a double-strand break in chromosomal DNA.

[16] A type of DNA repair that has a major role in generating chromosomal translocations is the non-homologous end joining pathway.

In order for the illegitimate joining of broken ends to occur, the exchange partners DNAs need to be physically close to each other in the 3D genome.

Chromosomal reciprocal translocation of the 4th and 20th chromosome .
Overview of some chromosomal translocations involved in different cancers, as well as implicated in some other conditions, e.g. schizophrenia, [ 8 ] with chromosomes arranged in standard karyogram order. Abbreviations:
ALL – Acute lymphoblastic leukemia
AML – Acute myeloid leukemia
CML – Chronic myelogenous leukemia
DFSP – Dermatofibrosarcoma protuberans
Human karyotype with annotated bands and sub-bands as used for the nomenclature of chromosomal abnormalities. It shows dark and white regions as seen on G banding . Each row is vertically aligned at centromere level. It shows 22 homologous autosomal chromosome pairs as well as both the female (XX) and male (XY) versions of the two sex chromosomes .
Further information: Karyotype