Mise en évidence de variations saltatoires de l'ADN nucléaire dans et entre les espèces du genre Medicago L.

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Abstract
Forty-two samples representing 20 Medicago L. species were used to determine the nuclear DNA content of each species. Significant intra- and inter-specific variations were evident. The total amplitude of these variations at the 2C level ranged from 1.6 to 9.4 pg, but the maximum significant DNA evolutionary value amounted to 7.2 pg only (Medicago sativa 4x). The occurrence of two nuclear populations from a number of origins was interpreted as corresponding to a fundamental evolutionary value for one of them and to the addition of metabolic DNA for the other. All the values observed were near multiples of a DNA quantum called a "nucleon," which was estimated to be 0.37 pg at the 2C level. This value corresponds to the lower DNA content observed in Angiosperms. Lastly, it appears that the arithmetical distribution of one nucleon among the usual 2n = 16 chromosomes in the genus ascribes a DNA amount of 0.02 pg to each chromatid, the approximate value for a chromosome modulus.Key words: Medicago, DNA content, nucleon, chromosome modules, saltatory genomic evolution.[Journal translation]