INFLUENCE OF HETEROCHROMATIN ON CHIASMA LOCALIZATION AND TERMINALIZATION IN MAIZE

Microsporocytes of two maize cultivars were submitted to C banding; in order to determine the effect of heterochromatin on chiasma localizat ion and terminalization. Chiasma position was evaluated during diplote ne and diakinesis in 14437 bivalents, 2993 of which were heterozygous for bands. Chiasma frequency was higher during diplotene in both culti vars, with a predominance of interstitial chiasmata located in euchrom atin. During diakinesis there was a reduction in chiasma. frequency in euchromatin, with a consequent increase in the heterochromatin region , suggesting chiasma terminalization. The chiasmata localized in euchr omatin appear to move to the region of the heterochromatin blocks. The heterochromatin, however, seem to serve as a barrier against terminal ization since terminalization beyond the bands was not observed in any heteromorphic bivalent.