Nucleotide Sequence Organization in Plant Chromosomes and Evidence for Sequence Translocation during Evolution

In higher-plant chromosomes, there is a considerable excess of DNA over that which constitutes the coding sequences (reviewed in Flavell 1980). The organization and evolution of this DNA has been a topic of considerable interest over the last few years. The most detailed and extensive information is available for the genomes of wheat, rye, barley, and oats, four species that have evolved from a common ancestor (Flavell et al. 1977). Most, but not all, of the additional DNA consists of sequences that are repeated from ten to more than a million times in the genome. The structures and arrangements of repeated sequences in plant genomes and comparisons of the repeated sequences present in the wheat, barley, rye, and oats genomes suggest a model for (1) the origin of the sequence organization patterns found in chromosomes and (2) how these patterns change during evolution (Flavell et al. 1979, 1980). In the...