Cytogenetics of Vicia. I. Male meiotic system in twelve species.

Abstract

Male meiosis investigated in twelve species of Vicia revealed that all the three gametic numbers (n=5, 6, 7) reported so far, in the genus, were present. Majority of them showed regular occurrence of 5, 6, 7 bivalents at diakinesis and metaphase I. The univalents, observed in some species, never exceeded two in number. The chiasma distribution was generally random and their frequency in each bivalent was dependant on the chromosome length. However, in V. hybrida, due to localization of chiasmata at distal ends in 5 out of 6 bivalents, the chiasma number was never more than two per bivalent. Highest recombination index was in V. faba and lowest in V. hybrida and in the former the terminalization occured very late. The three size classes among bivalents in PMC complements of various species and even the position of centromeres in bivalents could be clearly earmarked. The species differed markedly in overall chromosome size and on this basis they could be divided into four major groups. The distribution of chromosomes at anaphase I was normal in all the species. It is concluded that the gametic numbers of 5 and 6 are derivatives of n=7. The variation in gametic numbers, localization of chiasmata, pericentric inversions, differential chromosome size in various species and gene mutations might have played a significant role in speciation in the genus.