The late stage of prophase in meiosis in which the paired homologous chromosomes begin to repel each other and move apart, but are usually held together by chiasmata. The chiasmata are associated with breakage of two chromatids at corresponding points followed by refusion of the broken ends with exchange of segments between the chromatids; this is considered to be the cytologic basis for the crossing-over of genes. [diplo- + G. tainia, band]
