A cytological demonstration of "genetic" crossing-over

Abstract
A stage in meiosis where the paired chromosomes form loops, coming together at points distributed at random along their length, was first described by Rückert (1892) inPristiurus. These points we now recognise in suitable material as exchanges of partner amongst the four pairing half-chromosomes. But although Rückert did not appreciate this detail of structure he grasped the possible significance of their relationship: "Die bei der Reifung der Geschlechtzellen eintretende Verklebung Vorhergetrennter Chromosomen bezweckt einer Substanzaustausch derselben." He considered that here was the possibility of a chromosome "amphimixis," carrying a step farther Weismann's idea of nuclear "amphimixis." Similarly Correns (1902) and Boveri (1904, Contrary to his earlier view) foresaw the possibility of different parts of a chromosome behaving independently at meiosis. The discovery of linkage by Bateson, Saunders and Punnett in 1905 was a verification of these predictions, although not at first interpreted in this sense.

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