Chromosome Morphology and Meiosis in Some Eu-sorghums

Abstract

Detailed analysis of chromosomes at pachytene and later stages of meiosis were made in five species of Sorghum belonging to the Sub-genus Eu-Sorghum. Pachytene chromosomes are depicted on the basis of relative length, centromeric position, arm ratio and number of chromosomes which are adjoining the darkly staining region. The idiogram of all the five species which is represented diagramatically do not exhibit much variation. Pachytene chromosomes exhibit differentially staining regions which persists till late diakinesis. The nucleolus organizer in all the Eu-sorghums so far studied, is situated on the short arm of the first chromosome close to the centromere except for the species S. arundinaceum were it is located on the long arm. The possible cause for such difference is discussed.Studies on the pairing properties of the differentially stained regions show that synapsis starts from proximal to the distal end and separation of split chromosomes starts from the distal and proceeds to the proximal. The distribution of chiasmate at different stages was studied. The average frequency of chiasmata per cell between different species show no significant difference. A critical analysis of the bivalents at diakinesis revealed that chiasmata are absent or rarely present in the deeply staining region. If such a localization prevails, it would mean, recombination of the genes located in the heavily stained regions would be highly restricted, to the non-staining regions. Based on the idiogram of the pachytene chromosomes the possible role of chromosomes in speciation and the relationship between species are discussed.