Chromosomal Translocation

Chromosomal translocations occur when segments of one chromosome are relocated to another. They result from chromosome breakage and fusion (Fig.  1). Three breaks in a single chromosome lead to an intrachromosomal translocation, in which the translocated segment might be inverted. Single breaks lead to other chromosomal changes (Fig.  1). Reciprocal translocations occur when two nonhomologous chromosomes exchange segments. Translocations of chromosomal segments to the end of the chromosome also occur. This type of terminal translocation might account for the existence of telomeric repeats within the chromosomal arms. Finally, Robertsonian events are an extreme form of translocation when two acrocentric chromosomes fuse to generate a metacentric.