After tetrad formation, crossing over occurs in pachytene stage. The non-sister chromatids of homologous pair make a contact at one or more points. These points of contact between non sister chromatids of homologous chromosomes are called Chiasmata (singularChiasma). At chiasma, cross-shaped or Xshaped structures are formed, where breaking and rejoining of two chromatids occur. This results in reciprocal exchange of equal and corresponding segments between them.
