The relatedness and evolution of repeated nucleotide sequences in the genomes of some gramineae species

Reassociation kinetics of sheared denatured DNAs from wheat, barley, rye, and oats at 60 C in 0.18 cm Na⁺ indicate that approximately 80% of these genomes consist of repeated nucleotide sequences, using hydroxylapatite chromatography to detect reannealed DNA. The remaining DNA appears to consist of sequences present in only one or a few copies per haploid genome. Studies on heterologous duplexes formed in vitro between the repeated sequence DNA fractions from each of the species in turn indicate that many of the families of repeated sequences in these cereals evolved from common ancestral sequences. The extent of heteroduplex formation and duplex thermal stabilities suggest a scheme for the evolution of these species which agrees with taxonomic and genetic evidence. Further analyses of these parameters indicate that many quantitative changes in the chromosomal complement of repeated sequences have occurred during divergence of these species.