THE CYTOLOGY OF THREE HYBRIDS INVOLVING HORDEUM JUBATUM L.: THE CHIASMA DISTRIBUTIONS AND THE OCCURRENCE OF PSEUDO RING-BIVALENTS IN GENETICALLY INDUCED ASYNAPSIS

Abstract

Three hybrids, two of Hordeum jubatum L. × Secale cereale L. var. Prolific, and one of H. jubatum × H. bulbosum L., were examined cytologically. The two genomes of H. jubatum showed autosyndesis in the H. jubatum × S. cereale hybrids. It was concluded, therefore, that H. jubatum has two closely related genomes.One of the H. jubatum × S. cereale hybrids displayed weak asynapsis. The H. jubatum × H. bulbosum hybrid, on the other hand, showed strong asynapsis, although the prophase pairing was almost complete. It was concluded that the asynapsis of this latter hybrid was due to interaction of genes of the H. jubatum and the H. bulbosum genomes.The chiasma distributions of the hybrids were tested for randomness by Gaul's formula. It was found that the chiasma distributions of the H. jubatum × S. cereale hybrids followed a random pattern, whereas in the H. jubatum × H. bulbosum hybrid the distribution was disturbed by a secondary effect. Cytological observations and theoretical considerations led to the conclusion that the occurrence of pseudo ring-bivalents had disturbed the apparent chiasma distribution in the H. jubatum × H. bulbosum hybrid. A theory of the origin of pseudo bivalents and an evaluation of Gaul's formula is presented.