Comparative genomics of plant chromosomes.

Abstract

Comparative genomics, the study of similarities and differences in structure and function of the hereditary information in different taxa, uses molecular tools to investigate notions that far preceded the discovery that DNA was the hereditary molecule. Vavilov’s (1922) “law of homologous series in variation” was an early suggestion of the possibility of underlying commonality in the genetic blueprints of different (plant) species. In plants, genetic analysis based upon morphological and isozyme markers provided early hints that the arrangements of genes along the chromosomes of various taxa may have retained parallels since their divergence from common ancestors. DNA-level investigations in diverse taxa point to two broad messages: (1) The small but essential portion of most plant genomes encoding genes evolves relatively slowly, with corresponding genes retaining recognizable DNA sequences and similar order along the chromosomes of taxa that have been reproductively-isolated for millions of years. (2) A wide range of factors, such as DNA sequence mobility, gene deletion, and localized rearrangements, are superimposed on the relatively slow tempo of chromosomal evolution and cause many deviations from co-linearity. (3) Genetic loci that account for common phenotypes in different taxa are often at corresponding genomic locations, and may represent orthologous genes or members of orthologous clusters of genes.