Metagenomics Aims to Learn About the Diversity of Organisms, Particularly

Metagenomics aims to learn about the diversity of organisms, particularly microbes that inhabit natural environments. J. Craig Venter, a key figure in the race to obtain the human genome sequence, and his colleagues pioneered this approach in a study that analyzed DNA obtained from microbes collected from the Sargasso Sea, an intensively studied, nutrient-impoverished part of the Caribbean lying to the southeast of Bermuda. (C. J. Venter, K. Remington, J. F. Heidelberg, A. L. Halpern, D. Rusch, J. A. Eisen, D. Wu, I. Paulsen, K. E. Nelson, W. Nelson, D. E. Fouts, S. Levy, A. H. Knap, M. W. Lomas, K. Nealson, O. White, J. Peterson, J. Hoffman, R. Parsons, H. Baden-Tillson, C. Pfannkock, Y.-H. Rogers, and H. O. Smith. 2004. Environmental genome shotgun sequencing of the Sargasso Sea. Science 304:66-74.)
-Refer to the paragraph on the Venter et al. paper and the accompanying table. How do you think expected genes were placed into the categories shown in the table?

A) by searching for open reading frames (ORFs) , especially those with translation start and stop sites
B) by searching for matches, especially of the predicted gene products, with previously identified gene products of known function
C) by expressing the cloned genes in E. coli and then running biochemical analyses of the products
D) by searching for similarity between ORFs and those in existing databases