the two resulting long arms may fuse. The result is a single, large chromosome with a metacentric centromere. This form of rearrangement is a Robertsonian translocation.

Robertsonian translocations may arise during meiosis I when the short arms of acrocentric chromosomes cluster together in the nucleolus. This clustering, mediated by the nucleolus organizer region present on the short arms, brings non-homologous chromosomes