Chromosome Morphology and Meiosis in Some Eu-sorghums

Abstract

Detailed studies of chromosomes at pachytene and later stages of meiosis were made of 5 species of Sorghum belonging to the sub-genus Eu-Sorghum. They are S. verticilliflorum, S. arundinaceum, S. dochna, S. saccharatum, and S. caudatum. The idiograms of all 5 species are similar. Pachytene chromosomes exhibit differential staining regions which persist until late diakinesis. The nucleolus organizer is located on the short arm of the first chromosome close to the centromere in all species except S. arundinaceum. In the latter species it is located in the long arm of the first chromosome. Studies of the pairing properties of differentially stained regions of the chromosomes show that synapsis starts at the proximal and proceeds toward the distal end; while separation of the split chromosome commences at the distal and proceeds to the proximal end. A study of bivalents at diakinesis suggests that chiasmata are absent or rarely present in the deeply staining regions of the chromosomes. If such localization of chiasmata is true, recombination of genes in the heavily stained region of the chromosomes must necessarily be highly restricted.