Cytological Evidence for Crossing-Over in vitro in Human Lymphoid Cells

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Science  17 Apr 1964:
Vol. 144, Issue 3616, pp. 298-301
DOI: 10.1126/science.144.3616.298


In human blood cells dividing in vitro two chromosomes are occasionally found intimately associated in a quadriradial configuration (Qr). A Qr by traditional interpretation is the result of chromatid interchange. Since the configurations in blood cells often are equal and symmetrical and are composed of homologous chromosomes, they are considered cytological evidence that somatic crossing-over may occur in mammalian cells.