Effect of B Chromosomes on Meiosis in Tetraploid Pearl Millet

Abstract

In order to study the meiotic effects of B chromosomes when they are present in a tetraploid background, B chromosomes were introduced into autotetraploid pearl millet by crossing tetraploids with B-carrying triploids. A majority of the eutetraploids in the second generation progeny of this cross had two types of Bs viz., standards and isos, both in varying numbers and present separately or in com-bination. As it is not possible to fix a model number to a plant, cell level analyses were carried out. The mean A chromosome chiasmata per cell was higher in the 4n B cell population compared to controls. Within the 4n B cell population those with Bs had more chiasmata than those without Bs. Independent of this effect on A chromosome chiasmata, B chromosomes had a quadrivalent enhancing effect as was evident from regression analyses of variance. It is pointed out that the chro-mosome pairing pattern in 4n B plants was as may be predicted. on the basis of information about the effect of Bs on meiosis in diploids.