Evolution of the genetic system in higher plants
2001
Khidir, M.O. (University of Khartoum, Shambat (Sudan). Faculty of Agriculture)
The internal facts which influence the frequency of genetic recombination in a species are called the genetic system. It includes the chromosomal machinery and the mode of reproduction, and has an evolutionary course of its own. This is expressed in variation in the nature of the balance between, fitness and flexibility. This variation is described in this paper, with particular reference to the genus Carthamus L. The presence in Carthamus of two basic chromosome numbers (x=10 and x=12), four groups of species with n=10,12,22 and 32 chromosomes and different levels of compatibility makes in an ideal genus for the study of genetic systems. Increase in chromosome number was accompanied with increase in recombination index and self-compatibility, and self-incompatibility was associated with lower chiasma frequency. There was lower recombination index in cross-fertilized species than in self-fertilized ones. It is concluded that factors which promote flexibility are associated with factors which restrict it
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