Abstract
Observations in T. reflexa an rod-shaped gemini at first metaphase favor the two-plane theory of crossing-over. Rod-shaped gemini at first metaphase commonly originate from gemini with one interstitial chiasma at diakinesis (diag. 1, figs. 1 and 6). Terminalisation of chiasmata thus commonly occurs after the major coil is established. On the basis of the one-plane theory as the result of this terminalisation of chiasmata in rod-shaped gemini, partial antitropy (diag. 1, fig. 7) should be found to occur frequently but was found rarely.
On the basis of the two-plane theory as the result of terminalisation without crossing-over partial antitropy (diag. 1, fig. 5) should be found rarely and as the result of terminalisation after crossingover but showing no interstitiat reversal in direction of coiling (the types shown in diag. 1 figs. 2 and 3) should be found frequently, both of which premises accord with the actual observations.
