English: Dynamic chromosome pairing. The term “pairing” describes the spatial juxtaposition of entire homologous chromosomes, allelic sequences, and/or homologous sequences at non-allelic locations. (A, B) Homologous chromosomes can exist as paired throughout their entire length and the relative activities of pairing and anti-pairing factors determine the degree of global chromosome pairing. (C) Local pairing and anti-pairing factors can affect pairing status of specific genes or chromosomal regions. Local “pairing centers” can nucleate global pairing, but it is unclear whether factors regulating local pairing are different from global pairing factors. (D–F) In some cases, centromeres or telomeres from homologs can pair or cluster with non-homologous chromosomes, while there is no pairing along chromosome arms