Absence of chiasmata from the heteromorphic region of chromosome I during spermatogenesis in Triturus cristatus carnifex

Analysis of squash preparations of spermatocytes from crested newts, Triturus cristatus carnifex, has shown that in most cells at least one large bivalent regularly fails to form chiasmata in one arm-pair. Feulgen microphotometry of diplotene and metaphase bivalents has shown that it is the largest bivalent in each cell which shows chiasma failure in one arm-pair. A C-banding technique which identifies chromosome I by virtue of a long, darkly stained region in its long arm, was used to confirm the absence of chiasmata from one arm-pair of the longest bivalent, and specifically from the darkly stained region. The achiasmate region which chromosome I exhibits during spermatogenesis, corresponds to the heteromorphic region of oocyte lampbrush bivalent I in which chiasmata never form. A possible correlation between the complete absence of crossing-over from the heteromorphic region and unusual cytological and molecular features which it exhibits, are discussed.