A bivalent is the association of two replicated homologous chromosomes having exchanged DNA strand in at least one site called chiasmata. Each bivalent contains a minimum of one chiasma and rarely more than three. This limited number (much lower than the number of initiated DNA breaks) is due to crossover interference, a poorly understood phenomenon that limits the number of resolution of repair events into crossover in the vicinity of another pre-existing crossover outcome, thereby limiting the total number of crossovers per homologs pair.[4]