Sequence organisation in barley and oats chromosomes revealed by interspecies DNA/DNA hybridisation

Summary

The organisation of the repeated and non-repeated sequences in barley and oats genomes has been investigated using the repeated sequences of the wheat, oats, barley and rye genomes as DNA probes. Labelled barley and oats fragments of different lengths (200 to > 7000 nucleotides were hybridised to the repeated sequence probes and the proportions of the labelled fragments re-naturing with the probe DNAs were determined. The average spacings of these sequences through the barley and oats genomes were inferred from the results together with the proportions of the genomes in which the renatured sequences are concentrated. Over 70 per cent of barley and oats DNAs belong to families of repeated sequences. The few copy or non-repeated sequences in these genomes have a mean length of around 700 nucleotide pairs and are interspersed between repeated sequences. These findings have enabled schematic maps of the barley and oats genomes to be drawn. Both genomes appear to be constructed mostly of short sequences with neighbouring sequences being distinguished by their repetition frequency (repeated or non-repeated) or their homology with different repeated sequence probes. Short non-repeated sequences interspersed with short repeated sequences are concentrated in regions occupying 50 to 60 per cent of the barley genome and 40 to 50 per cent of the oats genome. Most of the remaining DNA consists of tandemly arranged repeated sequences of different evolutionary origins. It is postulated that much of this complex repeated sequence DNA could have arisen from amplification of compound sequences each containing repeated and non-repeated sequences.