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(in genetics) the exchange of sections of chromatids that occurs between pairs of homologous chromosomes, which results in the recombination of genetic material. It occurs during meiosis at a chiasma.
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cross·ing over (krosґing oґvər) the reciprocal exchange of genetic material between homologous chromosomes, resulting in recombination; often specifically denoting exchange between nonsister chromatids of paired homologous chromosomes during the first meiotic division.Medical dictionary. 2011.