Abstract
1. In 98.2% of the MI cells of a translocation heterozygote of Acrida lata, one chiasma was formed in one of the 'interstitial segment' and the distal unequal segments were separated equationally at AI in 96.1% of the cells. No chiasma was found at MI in the other interstitial segment and no equational AI separation of the distal unequal segments of this pair. The result indicates a close relationship between crossing-over and chiasma formation.
2. Frequencies of chiasmata at diplotene and MI were compared using a heteromorphic bivalent in which partner chromosomes were different for a block of heterochromatin and a special trivalent in a socalled centric fusion heterozygote, respectively, of Acrida lata. Chiasmata at these two stages were equally frequent, showing that in the present case no reduction in number of chiasmata was accompanied by the process of terminalisation from diplotene to MI.
