Quantitative evolution of transposable and satellite DNA sequences in Picea species

Clones containing tandemly arranged repeats belonging to two distinct sequence families, (i) PAG004P22F (2F) and PAG004E03C (3C) or (ii) Ty3/gypsy- (8R; PAG004B08R) and Ty1/copia-like sequences (9R; PAG007F19R), were selected from a randomly sheared total genomic DNA library of Picea abies . The inserts were used as probes in dot-blot hybridizations to genomic DNA of P. abies, Picea orientalis , Picea pungens , and Picea pungens var. glauca. All these entities are diploid and share the same chromosome number (2n = 24), but the genome sizes differ largely. The redundancy (copy number per 1C DNA) of sequences related to each probe varied greatly between the genomes. No significant correlation was found between the genome size and the copy number of sequences in any family. The quantitative ratios varied greatly (in each genome) between the two families of satellite DNA, between the sequences that represented copia or gypsy retrotransposons, and between tandemly arranged sequences and retroelements as a whole, suggesting that there is no common factor that controls the quantitative evolution of repeats belonging to different sequence families during speciation in Picea.