ular change often vary among plant families and orders in a manner that violates the assumption of a simple molecular clock. Finally, protein-coding genes exhibit patterns of amino acid change that appear to depend on protein structure, and these patterns may reveal subtle aspects of structure/function relationships. Only comparative studies of molecular sequences have the resolution to reveal this underlying complexity. A complete description of the complexity of molecular change is essential to a full understanding of the mechanisms of evolutionary change and in the formulation of realistic models of mutational processes.

Support from National Institutes of Health Grants GM 45144 (to M.T.C.), GM 15528 (to B.S.G.) and GM 45344 (to North Carolina State University) is gratefully acknowledged. The order of authorship is listed alphabetically. All authors made an equal contribution to this article.


Bousquet, J., Strauss, S. H. & Li, P. (1992a) Complete congruence between morphological and rbcL-based molecular phylogenies in birches and related species (Betulaceae). Mol. Biol. Evol. 9, 1076–1088.

Bousquet, J., Strauss, S. H., Doerksen, A. H. & Price, R. A. (1992b) Extensive variation in evolutionary rate of rbcL gene sequences among seed plants. Proc. Natl. Acad. Sci. USA 89, 7844–7848.

Bowman, C. M., Barker, R. F. & Dyer, T. (1988) In wheat ctDNA, segments of ribosomal protein genes are dispersed repeats, probably maintained by nonreciprocal recombination. Curr. Genet. 14, 127–136.

Bulmer, R., Wolfe, K. H. & Sharp, P. M. (1991) Synonymous nucleotide substitution rates in mammalian genes: implication for the molecular clock and the relationship of mammalian orders. Proc. Natl. Acad. Sci. USA 88, 5974–5978.

Chapman, M. S., Suh, S. W., Curmi, P. M. G., Cascio, D., Smith, W. W. & Eisenberg, D. S. (1988) Tertiary structure of plant RuBisCO: Domains and their contacts. Science 241, 71–74.

Chase, M. W., Soltis, D. E., Olmstead, R. G., Morgan, D., Les, D. H., Duvall, M. R., Price, R. A., Hills, H. G., Qiu, Y.-L., Kron, K. A., Rettig, J. H., Conti, E., Palmer, J. D., Manhart, J. R., Sytsma, K. J., Michaels, H. J., Kress, W. J., Karol, K. G., Clark, W. D., Hedren, M., Gaut, B. S., Jansen, R. K., Kim, K.-J., Wimpee, C. F., Smith, J. F., Furnier, G. R., Straus, S. H., Xiang, Q.-Y., Plunkett, G. M., Soltis, P. S., Swensen, S. M., Williams, S. E., Gadek, P. A., Quinn, C. J., Equiarte, L. E., Golenberg, E., Learn, G. H., Jr., Graham, S. W., Barrett, S. C. H., Dayanandan, S. & Albert, V. A. (1993) Phylogenetics of seed Plants: an analysis of nucleotide sequences from the plastid gene rbcL. Ann. Mo. Bot. Gard. 80, 528–580.

Christopher, D. A. & Hallick, R. B. (1989) Euglena gracilis chloroplast ribosomal protein operon: a new chloroplast gene for ribosomal protein L5 and a description of a novel organelle intron category designated group III. Nucleic Acids Res. 17, 7591–7608.

The National Academies of Sciences, Engineering, and Medicine
500 Fifth St. N.W. | Washington, D.C. 20001

Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement