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We have compared the restriction patterns and copy numbers of ribosomal RNA genes (rDNA) between and within individuals of Vicia faba. While the Eco RI blot-hybridization patterns changed only after one to two generations, copy number changes were found among different tissues of the same plant. Copy number differences among individuals in the population were as great as 95-fold, whereas as much as a 12-fold variation was seen among tissues of the same plant. Among individual F₁ progeny from genetic crosses, nearly an 8-fold variation was seen, and among individuals of the F₂ generation a spread of 22-fold was measured. Among individual siblings of self-pollinated parents, up to 7-fold variation was observed. However, changes in copy number did not necessarily indicate changes in rDNA Eco RI blot-hybridization pattern, and vice versa. Furthermore, nearest neighbor analysis of R-loop …