Chromosome Inconstancy in Zephyranthes mesochloa Baker

Abstract

1. Detailed karyotype analysis of Zephyranthes mesochloa has been made. In the normal complement, 2n=24 chromosomes have been observed in the present investigation, whereas previous study in the same species has shown 2n=48 chromosomes. The significance of this difference has been discussed. Previous record of chromosome numbers in the genus Zephyranthes has been reviewed. The lowest and the highest number recorded in this genus are 2n=12 and 2n=120 respectively.
2. Extensive numerical variation in the somatic chromosome complements has been noticed in Z. mesochloa, including both hypodiploid and hyperdiploid numbers which range from 2n=7+1 fragment to 2n=102. In addition, occurrence of structural chromosomal alterations in the somatic complements has also been noted. The mode of origin of these numerical and structural alterations has been discussed in the light of previous data in the present and other species of this genus as well as other genera of asexually reproducing plants.
3. Non-disjunction and endomitotic replication affecting all or several chromosomes of the complement have been suggested as possibly responsible for their origin. The evolutionary importance of such somatic alterations in species reproducing through vegetative means has been pointed out.