iGen3 16-18

Robertsonian Translocation

    A Robertsonian translocation occurs when fragments from non-homoloous chromosomes recombine in such a way that a single centromere is retained. In the example, a break in the p arm of the shorter chromosome allows a large acentric fragment from the q arm of the longer chromosome to recombine with it. The reciprocal product would combine the the small p arm of the longer chromosome with a small acentric fragment.

     Robertsonian fusions combine the long arms of two telocentric chromosomes: the tiny short arms are lost, and the result is a conservation of arm number with a reduction in chromosome number (counted from centromeres). That is, the karyotype 'loses' two telocentric chromosomes and 'gains' a single metacentric chromosome. [A Robertsonian fission occurs when a metacentric chromosome breaks at the centromere, such that the two arms segregrate independently as telocentrics].

    Note that the gene content is largely conserved. The translocated metacentric chromosome may pair with the two separate telocentric chromosomes, and if the three centromeres separate properly two balanced gametes will result. If two translocation gametes unite, the offspring will inherit the translocation in a stable manner.

Figure 2010 PJ Russell, iGenetics 3rd ed.; all text material 2013 by Steven M. Carr