Homologous somatic pairing

Somatic pairing of homologous chromosomes is similar to pre- and early meiotic pairing (see article: Homologous chromosome#In meiosis), and has been observed in Diptera[1] (Drosophila), and budding yeast,[2] for example (whether it evolved multiple times in metazoans is unclear[3]).

Mammals show little pairing apart from in germline cells, taking place at specific loci, and under the control of developmental signalling (understood as a subset of other long-range interchromosomal interactions such as looping, and organisation into chromosomal territories).

[5] In 1998 it was determined that homologous pairing in Drosophila occurs through independent initiations (as opposed to a directed, 'processive zippering' motion).

[4][8] The first RNAi screen (based on DNA FISH[9]) was carried out to identify genes regulating D. melanogaster somatic pairing in 2012,[10] described at the time as providing "an extensive “parts list” of mostly novel factors".

[5] An earlier RNAi screen in 2007 showed the disruption of Topoisomerase II activity impairs somatic pairing within Drosophila tissue culture,[11] indicating a role for topoisomerase-mediated organisation (or the direct interactions of topoisomerase enzymes) in pairing.