The Cytological Behaviour of B-chromosomes in Pennisetum typhoides

Abstract

In Pennisetum typhoides the B-chromosomes are smaller than the smallest A-chromosomes of the set and usualty lie at the periphery of the metaphase plate at mitosis. There is variation in the number of B's in the cells of the same root tip as also in the pollen mother cells of the same anther, flower and inflorescence. At pachytene the centromere was observed to be subterminal, the entire short arm is heterochromatic and the long arm has a short proximal heterochromatic region followed by light staining euchromatic region with eight chromomeres distributed along its whole length. B's regularly pair among themselves and when present in numbers of 3 or 4 form multivalents at diakinesis and metaphase I. They exhibit non-disjunction and precocious division at anaphase I, in the pollen mother cells. The differences between the B's present in this material and the accessories reported by Powell and Burton (1966) have been discussed.