The term "chiasma" is linked, if not identical, to chromosomal crossover. Each bivalent contains a minimum of one chiasma and rarely more than three. At this stage, non-sister chromatids may cross-over at points called chiasmata (plural; singular chiasma). The contact between two chromatids that will soon undergo crossing-over is known as a "chiasma". In meiosis, absence of a chiasma generally results in improper chromosomal segregation and aneuploidy. Chiasma frequency was scored at the later diplotene-diakinesis stages of meiosis. Other studies, however, indicate that chiasma, while supportive, are not essential to meiotic chromosome segregation.