Separase cleaves the cohesion molecules that hold the sister chromatids together to activate anaphase. Condensed chromosomes consist of two sister chromatids joined at the centromere. Sister chromatids remain attached during telophase I. Instead, they remain tightly associated with the centromeres of non-disjoined sister chromatids. Sister chromatid exchange (SCE) is the exchange of genetic information between two sister chromatids. Nonsister chromatids of homologous chromosomes may exchange genetic information over regions of homology. I and then the sister chromatids in meiosis II. As a result, each chromosome consists of two sister chromatids held together at the centromere. The two chromatids are joined at the centromere. The microtubules then contract to pull the sister chromatids of each chromosome apart. A bivalent is one pair of chromosomes (sister chromatids) in a tetrad. Sister chromatids at this point are called "daughter chromosomes". SDSA recombination involves information exchange between paired homologous chromatids, but not physical exchange. SDSA recombination involves information exchange between paired non-sister homologous chromatids, but not physical exchange. This allows the sister chromatids to remain together while homologs are segregated.