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Pachytene (Pachynema): Comparatively longer phase. Bivalent chromosomes split
into similar chromatids. This stage is called tetrads. This is characterised by the
appearance of recombination nodules at which crossing over occurs. Crossing over
is the exchange of genetic material between non-sister chromatids of two homologous
chromosomes with the help of an enzyme, recombinase. It leads to recombination of
genetic material on the homologous chromosomes. Recombination is completed by the
end of pachytene.