Nucleotide sequence organisation in the wheat genome

Abstract

Chromosomal nucleotide sequence organisation has been studied in hexaploid wheat, Triticum aestivum, using methods based upon the different renaturation kinetics of repeated and non-repeated sequences. Approximately 25 per cent of the wheat genome consists of non-repeated sequences. Nearly two-thirds of these (15 per cent of the genome) are around 1000 base pairs long interspersed between repeated sequences. Approximately 7 per cent of the genome consists of non-repeated sequences several thousand base pairs long. Less than 5 per cent of the genome consists of very much longer non-repeated sequences. Four per cent of the genome consists of extremely rapidly renaturing (fold-back ?) sequences. These sequences are distributed through at least 20 per cent of the genome. Between 50 and 65 per cent of the genome consists of repeated sequence DNA which is cleaved to duplexes approximately 400 to 800 base pairs long by S1 nuclease after renaturation in vitro. This implies that related repeated sequences frequently have different neighbouring sequences in the chromosomes. Repeated sequences (32 per cent of the genome) able to reanneal in very stringent incubation conditions are between approximately 350 and 650 base pairs long and are distributed through 85 per cent of the genome at intervals of less than 4000 base pairs. This distribution implies that short regions of essentially non-diverged repeated sequence DNA are interspersed with longer regions of diverged repeated sequence DNA in the chromosomes. Approximately 10 per cent of the genome appears to consist of very long repeated sequences or of long clusters of short, essentially identical repeated sequences.