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The stage of prophase in meiosis in which pairing of homologous chromosomes is complete and the paired homologues may twine about each other as they continue to shorten; longitudinal cleavage occurs in each chromosome to form two sister chromatids so that each homologous chromosome pair becomes a set of four intertwined chromatids.
[pachy- + G. tainia, band, tape]
Etymology: Gk, pachy + nema, thread
the postsynaptic tetradic chromosome formation that occurs in the pachytene stage of the first meiotic prophase of gametogenesis.