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Trends of chromosome evolution in family commelinaceae


, : Trends of chromosome evolution in family commelinaceae. Nucleus (Calcutta) 27(3): 231-241

Taxa (24) belonging to 12 spp. under 8 genera, representing members of both the tribe Commelineae and Tradescanticae, were studied. Different populations belonging to the representative species were collected. In view of the profuse vegetative propagation and almost obsolete sexual reproduction in the family, a study of the population-wise differences in these species was called for, both in the finer details of chromosome structure and behavior and the phenotypic differences, if any, among populations growing in different areas of the subcontinent. Three sizes of chromosomes have been observed among the taxa studied, the smallest being in Murdannia, medium sized in Commelina and culminating in the long chromosomes of Callisia, Rhoco, Setcreasea and Zebrina. Commelineae and Tradescanticae are characterized by 2 haploid sets of chromosomes; the former having x = 10, 11, 12, 13 and 15 or multiples of them and the latter mostly x = 6 with occasional polyploidy. There is a remarkable constancy in chromosome number commenlinaceae in spite of minor phenotypic differences and wide distribution in various climatic zones. The constancy of the particular chromosome set might have some adaptive value leading to selective advantage. In Commenlineae, there are minute karyotypic differences as evidenced by their karyotype formula, along with evidences of polyploidy. Both polyploidy and structural alteration have been effective in the evolution of species as well as intraspecific genotype. A study of the karyotypes in Tradescantieae indicates that rearrangement of chromosome segments has played a significant role in the evolution of populations. Such rearrangement may lead to non-homology of segments giving rise to univalents noted in meisois. Structural alterations and possibly hybridity have affected the number of chromosomes with secondary constriction. Tradescantieae has a distinct karyotype, which had undergone considerable alteration and rearrangement during evolution. Cryptic changes in karyotypes have been responsible for the origin of intraspecific races. In both tribes, the various populations studied showed a constancy in chromosome number with a marked change in their chromosome structure. These changes may be minute rearrangements of chromosome parts in certain taxa and addition or dejection of segments in the other. These, along with polyploidy and hybridization, may be responsible for the evolution of new strains. Populations or intraspecific races. The 2 must have diverged quite early during the evolution of the family.

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