DNA variation between and within chromosome complements of Vicia species

Abstract

2C Nuclear DNA amounts in diploid species of the genus Vicia (x = 5, 6, and 7) range from approximately four to twenty seven picograms. The DNA amount varies independently of the chromosome number and of taxonomic grouping within the genus. Comparisons of the distribution of DNA amounts among chromosomes within the complements show that increase in total nuclear DNA amount within the genus is achieved by equal increments to each chromosome independent of size i.e., small chromosomes acquire the same amount of extra DNA as the large chromosomes. An inevitable consequence of such a pattern of DNA change is that the chromosomes within complements with high DNA amount are more alike in size and DNA content, more symmetrical, than within complements of species with low DNA amount. In a few species the symmetry is confounded as a result of Robertsonian fusion. The equal distribution of extra DNA among chromosomes within a complement has been reported in other genera of flowering plants viz. in Lolium, Festuca and Lathyrus. In all cases there is evidently a severe constraint either upon the way in which the nuclear DNA variation is achieved or else upon its persistence in the face of selection. Since the pattern of change affects the relative sizes of chromosomes within complements we conclude that relative size may itself be of adaptive importance. © 1983, The Genetical Society of Great Britain.