Reciprocal and Robertsonian translocation

Reciprocal translocation: When two non-homologous chromosomes exchange segments. There is one recurrent reciprocal translocation between chromosome 11 and chromosome 22 but most of them are unique for each family. Individuals who carry a balanced reciprocal translocation are most often phenotypically normal because all the genetic material is present. However, due to a risk of unbalanced segregation of the translocation chromosomes during meiosis, there is an increased risk of spontaneous abortions and/or the birth of an affected child with an unbalanced translocation.

Figure 1: Reciprocal translocation

Robersonian translocation: When two acrocentric chromosome breaks near the centromeres and rejoin in a way that results in the fusion of the two q arms (the Robertsonian translocation) and loss of the p arms. The acrocentric p-arms are mostly composed of repetitive DNA, but they also contain our clusters of ribosomal RNA genes. However, since we have ten such clusters the loss of two has no phenoytypic consequence. Hence, individuals who carry a balanced Robertsonian translocation are phenotypically normal, but they can experience spontaneous abortions or infertility.

Figure 2: Robertsonian translocation