Nuclear DNA variation in Tephrosia

Abstract

2C nuclear DNA amounts and chromatin areas were estimated in twenty diploid and tetraploid (2n = 22, 44; x= 11) species of the genus Tephrosia. There were significant differences between the species both in DNA content and chromatin area. The divergence and evolution of Tephrosia species was accompanied by large scale quantitative DNA variation, ranging from 1.3 picograms in T. strigosa to 7.4 in T. pumila, and the DNA amount varied independently of the chromosome number. The element of discontinuity in the distribution of DNA changes between complements was quite regular. The species fell into eight distinct cluster groups with an interval of 0.74 pg between the two adjoining groups. In the light of the karyotypic and nuclear DNA differences between T. leptostachya, T. hamiltonii, T. wallichii and T. purpurea, T. incana and T. villosa, T. subtriflora and T. multiflora, there is indeed a case for considering them as separate species and not synonyms of T. purpurea, T. villosa and T. multiflora. DNA density increased with increase in DNA contents. As expected, the DNA content of colchitetraploids (Co, C1, C2) was almost double to the amount present in their corresponding diploids.

Genome size variation in the North American sunfish genusLepomis(Pisces: Centrarchidae)

“…Genome sizes are normally distributed within species (both in terms of measurements (nuclei) and DNA values of individuals within populations), and continuously distributed across species. As noted by Gold & Amemiya (1987), this pattern of continuous genome size change appears to typify many animal groups (Bachmann et al 1972(Bachmann et al , 1985Bianchi et al 1983;Johnson et al 1987) and differs markedly from the discontinuously distributed species DNA values found in many plant groups (Narayan, 1983;Cavalier-Smith, 19856;Sims & Price, 1985;Raina et al 1986;Labani & Elkington, 1987). In the latter, many species or species-groups are differentiated by quantum differences in genome size which is not attributable to polyploidy.…”

DNA amounts and chromatin compactness in Vicia

“…The phenomenon of discontinuous variation of DNA amounts, surprisingly following a consistent pattern, suggests that only certain quanta of DNA are tolerable in terms of fitness and survival, and the perusal of earlier literature shows that such a series of 'quantum jumps' in DNA is not uncommon. It has been reported in a number of other genera (Rothfels et aZ, 1966;Narayan & Rees, 1976;Narayan, 1982;Sparrow & Nauman, 1973;Raina et al, 1986) and the group means, as in Vicia, occur at the intervals of approximately 2 pg in Clarkia and Nicotiana, and of approximately 1 in Tephrosia and 4 in Allium and Lathyrus. There is evidence, therefore, to suggest that divergence and evolution of species is not only accompanied by DNA variation and change in the composition of DNA but also by a rigid constraint, leading to constant increment in DNA amounts between DNA groups.…”