qWO previous studies have provided extensive tetrad data on crossing-over in the centromere region of linkage group I. LINDEGREN and LINDEGREN (1942) found an excess of multiple exchanges across the centromere. These multiple exchanges included a proportion of %strand pairs in excess of the 0.25 expected if all four chromatids participated in exchanges at random. Such a deviation might be attri...

NTIL comparatively recently there has been no compelling evidence U that genetic “interference” involves more than the occurrence of one crossover reducing the chance of another occurring in nearby regions. Genetic data from Drosophila have generally been interpreted as indicating that there is no “chromatid interference,” that is, that a crossover between two of the four chromatids does not in...

This study concerns the retinotopic organization of the ganglion cell fibres in the visual system of the frog Xenopus laevis. HRP was used to trace the pathways taken by fibres from discrete retinal positions as they pass from the retina, along the optic nerve and into the chiasma. The ganglion cell fibres in the retina are arranged in fascicles which correspond with their circumferential posit...