This family consists of several Barren protein homologs from several eukaryotic organisms. In Drosophila Barren (barr) is required for sister-chromatid segregation in mitosis. barr encodes a novel protein that is present in proliferating cells and has homologs in yeast and human. Mitotic defects in barr embryos become apparent during cycle 16, resulting in a loss of PNS and CNS neurons. Centromeres move apart at the metaphase-anaphase transition and Cyclin B is degraded, but sister chromatids remain connected, resulting in chromatin bridging. Barren protein localizes to chromatin throughout mitosis. Colocalization and biochemical experiments indicate that Barren associates with Topoisomerase II throughout mitosis and alters the activity of Topoisomerase II. It has been suggested that this association is required for proper chromosomal segregation by facilitating the decatenation of chromatids at anaphase. This family forms one of the three non-structural maintenance of chromosomes (SMC) subunits of the mitotic condensation complex along with Cnd1 and Cnd3.